I bought it today. From what I've read, here's my take on 4e, mostly from the character sheets:
-- Starts at about 2nd-3rd level in offensive power (in the terms of earlier editions), with a slow drip of power increases. A 2nd level character is perhaps 1/6th more effective than a 1st level character, not ~ 1/3 to 1/2 more effective as in 3e. (I'm basing this on additional hit points and abilities gained. So levels are perhaps half value or 1/3 value.
--- Starting a higher level is good for most people. Most people don't like having a character who is threatened by every blow and uses up their abilities in one shot. I actually like the old ways better, as I'm more of a "realist" about combat (I like Boot Hill where you have a 1/6 chance of dying everytime you get shot) and I like the resource management aspects of editions 1-3.
--- Staying in the 2nd-8th level range longer by starting there and ramping down level progression is good. I'm one of those who thought 3e was a crazy, broken superhero game above a certain level (~ 13th) and was most fun in the middle levels. I'd bet most people enjoy the "powerful but not a superhero" stuff, so this is probably a good change from 3e -- more of a reset to AD&D where levels took longer and tended to not get so high (pace the folks who played AD&D as 12 year olds and remember as it being about 157th level mages who conquered the universe -- that'll happen in any edition).
-- No longer a simulation of anything but itself. D&D started out from Chainmail, which was meant to be a realistic simulation of medieval warfare. Fighters did what fighters did in medieval times -- wear armor, swing weapons, fire bows, kill and be killed. The fighter class, for the first time since Chainmail, has been deleted in all but name. The fighter has now has magical power of healing and of mind controling enemies into attacking them. But wait, it doesn't mention magic or psionics to explain what a Healing Surge is or what it means to Mark an Opponent. Perhaps there is fluff to explain it in the PHB, but the key thing is that these powers are not attempting to replicate a real life situation or even something typically seen in Tolkienesque or Conanesque fantasy literature. Instead, they are game rules made because WOTC thinks they make the game work well, no OUTSIDE the game reason. That's a huge shift of logic, at least for me.
--- If D&D 4e is simulating anything, it's simulating computer gaming. Perhaps necessary, but to me, sad.
--- That's just my take on the Fighter. The Rogue seems fairly normal. The Wizard is just uppowered -- 3rd level instead of 1st -- and nicely gets lots of free, automatic spells -- Light and Magic Missile at will. No more resource management needed for the basics.
-- Simplification. I haven't seen the PHB yet, so I don't know if the Cleric and Wizard spell choices are dictated by the rules (everyone must have have Magic Missile, Sleep, etc.) or if that's a choice made for the pre-gens. From earlier editions, they did choose the most effective straight-at-ya spells, so I don't really mind if there's not other spell choices.
--- Having everything spells out in detail on the character sheets is really nice. Hopefully, we will be able to get PDF's or something when making characters from the D&D website.
--- The sad part is that writing all that out manually would be too tedious to do now -- pushing D&D to be a computer game, even if played in person.
--- Before Gary Gygax died, one of his complaints about 3e was that it was just too darn complicated and therefore not as open to new players. It looks, so far, as if WOTC has taken that criticism to heart and tried to make a 3e Basic.
Overall, my review is:
-- Valliant effort by WOTC to improve the game by looking at the key issues of correcting the power curve (starting and keeping things in the 2nd-8th level range longer), game play where resource management is no longer key, and simplification.
-- I'm sure it will be fun to play.
-- The threat to all editions of getting gummed up by splatbooks and extra rules is even more important for a simplified game supposedly open to new players.
-- To me, I'm seeing a game that's something like 60% D&D and 40% new content, with a setting that's 60% Gygaxian and 40% something else. Dragonborn ain't real D&D. Nothing wrong with new games, but I'm sad the old game is no longer being made.
So, I won't object to trying it out when my old DM moves back to town and wants to restart his game (probably a month or two more).
But in my own campaign, I'm sticking with 3.5e for now.
We'll see what's in 4e PHB, but I'm thinking converting is not a real option. I've got 27 years of AD&D and 3.5e content running around in my Greyhawk world, and I don't feel like retconning in total different variants of all the old retired guy and NPC's and semi-dormant campaigns, not to mention adding Dragonborn and whatever lameness awaits in the full books, so I think I'm on my own, just as if D&D had gone belly up and out of business. In a real sense, for old school gamers, I think it has. Good thing I've got like 5 PHB's . . . and I guess if my DMG gets lost or something, use ones will abound for years, as most people will go with the flow and switch over.
The only downside to playing 4e and running 3.5e is the brain space and confusion that can result. But I guess since I've done Mac and PC for years, and I can mouse with both hands, I should be able to keep two D&D OS's straight.
So who's predicting 5e? I'm thinking 2012, and looks like 50% 4e, 25% re-adding 3.5 stuff that will be added to 4e in later supplements, and 25% new stuff from computer games. Maybe that will be called 4.5e, though . . .
-- Starts at about 2nd-3rd level in offensive power (in the terms of earlier editions), with a slow drip of power increases. A 2nd level character is perhaps 1/6th more effective than a 1st level character, not ~ 1/3 to 1/2 more effective as in 3e. (I'm basing this on additional hit points and abilities gained. So levels are perhaps half value or 1/3 value.
--- Starting a higher level is good for most people. Most people don't like having a character who is threatened by every blow and uses up their abilities in one shot. I actually like the old ways better, as I'm more of a "realist" about combat (I like Boot Hill where you have a 1/6 chance of dying everytime you get shot) and I like the resource management aspects of editions 1-3.
--- Staying in the 2nd-8th level range longer by starting there and ramping down level progression is good. I'm one of those who thought 3e was a crazy, broken superhero game above a certain level (~ 13th) and was most fun in the middle levels. I'd bet most people enjoy the "powerful but not a superhero" stuff, so this is probably a good change from 3e -- more of a reset to AD&D where levels took longer and tended to not get so high (pace the folks who played AD&D as 12 year olds and remember as it being about 157th level mages who conquered the universe -- that'll happen in any edition).
-- No longer a simulation of anything but itself. D&D started out from Chainmail, which was meant to be a realistic simulation of medieval warfare. Fighters did what fighters did in medieval times -- wear armor, swing weapons, fire bows, kill and be killed. The fighter class, for the first time since Chainmail, has been deleted in all but name. The fighter has now has magical power of healing and of mind controling enemies into attacking them. But wait, it doesn't mention magic or psionics to explain what a Healing Surge is or what it means to Mark an Opponent. Perhaps there is fluff to explain it in the PHB, but the key thing is that these powers are not attempting to replicate a real life situation or even something typically seen in Tolkienesque or Conanesque fantasy literature. Instead, they are game rules made because WOTC thinks they make the game work well, no OUTSIDE the game reason. That's a huge shift of logic, at least for me.
--- If D&D 4e is simulating anything, it's simulating computer gaming. Perhaps necessary, but to me, sad.
--- That's just my take on the Fighter. The Rogue seems fairly normal. The Wizard is just uppowered -- 3rd level instead of 1st -- and nicely gets lots of free, automatic spells -- Light and Magic Missile at will. No more resource management needed for the basics.
-- Simplification. I haven't seen the PHB yet, so I don't know if the Cleric and Wizard spell choices are dictated by the rules (everyone must have have Magic Missile, Sleep, etc.) or if that's a choice made for the pre-gens. From earlier editions, they did choose the most effective straight-at-ya spells, so I don't really mind if there's not other spell choices.
--- Having everything spells out in detail on the character sheets is really nice. Hopefully, we will be able to get PDF's or something when making characters from the D&D website.
--- The sad part is that writing all that out manually would be too tedious to do now -- pushing D&D to be a computer game, even if played in person.
--- Before Gary Gygax died, one of his complaints about 3e was that it was just too darn complicated and therefore not as open to new players. It looks, so far, as if WOTC has taken that criticism to heart and tried to make a 3e Basic.
Overall, my review is:
-- Valliant effort by WOTC to improve the game by looking at the key issues of correcting the power curve (starting and keeping things in the 2nd-8th level range longer), game play where resource management is no longer key, and simplification.

-- I'm sure it will be fun to play.
-- The threat to all editions of getting gummed up by splatbooks and extra rules is even more important for a simplified game supposedly open to new players.
-- To me, I'm seeing a game that's something like 60% D&D and 40% new content, with a setting that's 60% Gygaxian and 40% something else. Dragonborn ain't real D&D. Nothing wrong with new games, but I'm sad the old game is no longer being made.

So, I won't object to trying it out when my old DM moves back to town and wants to restart his game (probably a month or two more).
But in my own campaign, I'm sticking with 3.5e for now.
We'll see what's in 4e PHB, but I'm thinking converting is not a real option. I've got 27 years of AD&D and 3.5e content running around in my Greyhawk world, and I don't feel like retconning in total different variants of all the old retired guy and NPC's and semi-dormant campaigns, not to mention adding Dragonborn and whatever lameness awaits in the full books, so I think I'm on my own, just as if D&D had gone belly up and out of business. In a real sense, for old school gamers, I think it has. Good thing I've got like 5 PHB's . . . and I guess if my DMG gets lost or something, use ones will abound for years, as most people will go with the flow and switch over.
The only downside to playing 4e and running 3.5e is the brain space and confusion that can result. But I guess since I've done Mac and PC for years, and I can mouse with both hands, I should be able to keep two D&D OS's straight.
So who's predicting 5e? I'm thinking 2012, and looks like 50% 4e, 25% re-adding 3.5 stuff that will be added to 4e in later supplements, and 25% new stuff from computer games. Maybe that will be called 4.5e, though . . .