If you prefer tactical strategy games like Descent then 4E should be your cup of tea. If you prefer roleplaying games then run, don't walk, as far away as you can get.
Well, I enjoy tactical strategy games, and still prefer 3E. 4E mostly sacked the simulationist aspect of gaming, which I really didn't like. In terms of gamist aspects, it has more than 3E, but 3E already had ambiguous hp representation, non-sensical combat rounds (despite the initative, everything should all be happening roughly simultaneously over 6 seconds...yeah, right), and so on. 4E is attrative to gamist people mainly for not treating everything as equal in terms of the rules (NPCs work differently than PCs, even if they're the same race as the PC) and placing balance above most everything else in importance. Both of which make the game smoother and easier to DM.
But people who would call themselves mainly storytellers also often flock to it because...quite simply, DM fiat is hard-coded into page 42 of the DMG to resolve any issue that isn't a textbook use of a skill or power...or even sometimes when using it exactly as intended. A lot of people complain that 3E had rules for everything. Which is ridiculous and hyberbole, but it does have a lot of example DCs and numbers for things, examples of what size of modifer (often +/-2, sometimes 5, 8, 10...) is appropriate for circumstantial alterations, and tries its hardest to gve you the tools to compare whatever to. 4E simply has you base it on the characters' relative level, which I find grating. For a storyteller, I guess this is a good thing, the rules being completely and unarguably subject to what the DM wants so the plot can't be affected.
Anyway...
Pros:
*Easier/faster to prepare games, run encounters, and build characters
*Randomness in character generation is all but eliminated (contributes to Pro #1, and makes it so you never get a situation where you can't play a wizard like you wanted to because you rolled all 13's)
*Classes are more closely balanced at all levels of play than 3E
*Anyone can handle out of combat utility magic with just one feat (could also consider this a con)
*No longer need feats to add stats to their logical attack rolls. For example, light weapons use dex to hit, heavy thrown weapons use str
*Early levels are far less randomly deadly
*Players will have shorter rounds, and thus more rounds to act and do stuff. However, combat also takes far more rounds than 3E, so shorter combat does not exist as a pro.
*No save or die (though I recall a thread about a monster that had something nearly this)
*Less room to use system mastery and pre-game planning to succeed. I personally hate this, and I'm sure you know your players well enough to know if they will too, but the consensus seems to label it a pro.
Cons:
*The skill system is utterly gutted. I don't mind the combination of skills so much (though Perception seems like quite the no-brainer to get if you can), but the elimination of skills like craft irks me. The biggest issue, though, is the homogeny of training levels. Instead of individual ranks gained each level, you're either trained or not, the difference being a flat, unchanging 5 points. I like more variety in the levels of dedication. Also, EVERYONE gets better at a skill solely from leveling up, as you add 1/2 level to all skill rolls. Functionally, if you're always in level appropriate encounters, your chances of winning an opposed skill roll stay the same (enemies also get the 1/2 level). On unopposed skill checks, like climbing against a DC, it means you get better at climbing ven if you've never once practiced it before in your entire life. Just because you're an epic character, you can climb better than a low level climbing expert. So, they sacrificed major simulation elements for a "false gain" in gamist aspirations.
*Skill challenges apparently don't work. This gets a separate con, if only because the first con already went on so long
*Very twisted alteration of niche protection. In 3E, only rogues and the like can disable traps. Now anyone can. In 4E, only classes that get ranged powers should bother picking up a bow (unless you really have no other means of attacking at all). In 3E, lots of classes could become accomplished archers solely by using their own class resources (feats, buff spells). In 4e, if you want an archer or a TWF, better be a ranger...
*Punishing and limited multiclassing system. Instead of the freedom of 3E's system, in 4E you have to wait till level 11 and spend feats to gain a small smattering of the secondary class's features with limited use. There is no true multiclassing.
*Lack of rules for basic things. No table of hardness and hit points for breakable materials (up to the DM). At least in the core books, no disarm rules at all. Tripping is only available as class powers, it's somehow too complicated to be a basic attack available at will. Grappling doesn't really exist. You can hug a guy and struggle to keep him from moving, but you can't really beat him up with unarmed damage, pin him, etc... I forget, but I think he can even still attack other people around him!
*Too much combat focus. Very few powers have out of combat uses, and those that are get severe limitations in power or availability. There are rituals, but they tend to be expensive and take several minutes or more to cast. They will not help you on the spot.
*Harder to make "different" builds. The class powers list and the fact that many classes have pre-set builds that focus on one stat or another, with powers working based on said stats, tends to basically force you to be a "strength rogue" or "charisma rogue;" a "int warlord" or a "cha warlord," which makes it very hard to try something totally different. 3E kinda of needed splats, but eventually you could generally try just about anything with any class and do ok. A charisma fighter could focus on feats to intimidate better in combat, use cha to add to will saves, and give bard-like boosts to allies by being inspiring. A wizard could enter a fighter-mage prestige class, take Arcane Strike feat, and so on, and pool all his resources towards thumping things with his huge mallet (thanks to spells to enlarge himself, give him godly str, and wield an effectively collasal hamer). 4E is far more rigid in what each class can do.
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