My own thoughts based on what we've heard:
NO MORE LEVEL DRAIN - Good. I don't mind bad things happening to characters, and I don't mind scary things, but this always struck me as too big a punishment. 3.5 made it less so, but still...it doesn't contribute to the fun of the game for me.
NO MORE (temporary) ABILITY DRAIN - Mixed. It sucks to have that happen, and the record keeping is a pain, but on the other hand, this seems to succeed in giving the characters a real source of terror without being as heavy on the punishment as level draining. It seemed like a good compromise. I won't miss it though.
NO MORE SAVE-OR-DIE - Good. I hate spending a lot of time putting together a character and exploring it's development only to have it all end with one bad roll. When it happens in the beginning of a massive climatic battle it's not at all fun.
NO MORE ETHICAL ALIGNMENTS - Skeptical/ Bad. I don't think they're getting rid of ethical alignments. Personally, I'd rather they dropped alignments as a mechanic altogether and just offer a paragraph or two or roleplay suggestions. Having an alignment mechanic at all, even a dumbed down one doesn't appeal to me at all. I'll either have to choose my DM more carefully than usual or dump it altogether.
SNEAK ATTACK ON ANYTHING - Mixed. To me, it really depends on how the sneak attack mechanic works. I've never liked Sneak Attack in the past and I'm hopeful they made some changes to 4th ed. but I don't really know enough at this point to have a strong opinion.
FASTER GAME MECHANICS - Good. There's nothing wrong with making game play faster and more involving for all the players as well as the DM.
FASTER (N)PC CREATION - Good, if true. I believe that the NPC and Monster set-up times are improved...and that's great. PC creation, I am doubtful about. It'd be good if it were easier...the one thing I disliked most about the skill system in 3.5 is how complicated it is to create characters at higher levels.
NO MORE EXCESSIVE AMOUNTS OF MAGIC ITEMS - Best News Yet! Alas, I think they're going to weasel out on this one. If they drop the excessive amounts of Magic Items and especially the reliance on magic items to survive, I will be overjoyed. From little bits of offline rumors and hints in Insider articles, however, I think they've chickened out and backed away. Which means for me that if they don't lessen the reliance on magic items, that'll be the thing I dislike the most about the new system. I can hardly tolerate it with 3.5 now.
NO MORE (or less) VANCIAN CASTING - Good. I'm so tired of the vancian system it's not even funny. I'm not sure the power system is a good replacement, but I'm willing to give it a shot.
NO MORE SPELL SCHOOLS - Neutral. I don't know enough about the new system to have any opinion here.
FOCUS ITEMS - Neutral- As per above. Not enough information.
SKILL SYSTEM REVAMP - Mixed. I like simplifying the skills so that there aren't so many of them (Athletics for Jump, Climb, and Swim for example). But I don't want the skill system as a mechanic to be simplified to the point where you hardly use them, and I fear that's the direction they're going in. I'd much rather see something more similar to Iron Heroes.
BASIC RACES CHANGES - Good. I've liked everything I've heard so far. I won't miss the Gnome at all.
RACIAL PANTHEONS GETTING THE BOOT - Indifferent. I've only rarely used the published pantheons anyway. I prefer my homebrewed systems of religions.
ELIMINATION OF PRESTIGE CLASSES - Good. I'd far rather they focused on making core classes fun to play all the way through the advancement table.
EFFORT TO BALANCE FEATS - Good. I haven't heard anything bad about it yet. I hope they have a lot of racial and class linked feats.
PARTY ROLES - DEFENDER, LEADER, ETC. - Mixed. I don't mind it if it's to help people, especially beginners, design strong party dynamics. I will be very annoyed, however, if each role is required for a party. I don't want party design to be put into a box.
POINTS OF LIGHT SETTING DESIGN - Good. I like what I've heard, and even if I didn't, I'd design my own anyway.
LACK OF BACKWARDS COMPATIBILITY - Neutral. I don't really care that much.
NO MORE LEVEL DRAIN - Good. I don't mind bad things happening to characters, and I don't mind scary things, but this always struck me as too big a punishment. 3.5 made it less so, but still...it doesn't contribute to the fun of the game for me.
NO MORE (temporary) ABILITY DRAIN - Mixed. It sucks to have that happen, and the record keeping is a pain, but on the other hand, this seems to succeed in giving the characters a real source of terror without being as heavy on the punishment as level draining. It seemed like a good compromise. I won't miss it though.
NO MORE SAVE-OR-DIE - Good. I hate spending a lot of time putting together a character and exploring it's development only to have it all end with one bad roll. When it happens in the beginning of a massive climatic battle it's not at all fun.
NO MORE ETHICAL ALIGNMENTS - Skeptical/ Bad. I don't think they're getting rid of ethical alignments. Personally, I'd rather they dropped alignments as a mechanic altogether and just offer a paragraph or two or roleplay suggestions. Having an alignment mechanic at all, even a dumbed down one doesn't appeal to me at all. I'll either have to choose my DM more carefully than usual or dump it altogether.
SNEAK ATTACK ON ANYTHING - Mixed. To me, it really depends on how the sneak attack mechanic works. I've never liked Sneak Attack in the past and I'm hopeful they made some changes to 4th ed. but I don't really know enough at this point to have a strong opinion.
FASTER GAME MECHANICS - Good. There's nothing wrong with making game play faster and more involving for all the players as well as the DM.
FASTER (N)PC CREATION - Good, if true. I believe that the NPC and Monster set-up times are improved...and that's great. PC creation, I am doubtful about. It'd be good if it were easier...the one thing I disliked most about the skill system in 3.5 is how complicated it is to create characters at higher levels.
NO MORE EXCESSIVE AMOUNTS OF MAGIC ITEMS - Best News Yet! Alas, I think they're going to weasel out on this one. If they drop the excessive amounts of Magic Items and especially the reliance on magic items to survive, I will be overjoyed. From little bits of offline rumors and hints in Insider articles, however, I think they've chickened out and backed away. Which means for me that if they don't lessen the reliance on magic items, that'll be the thing I dislike the most about the new system. I can hardly tolerate it with 3.5 now.
NO MORE (or less) VANCIAN CASTING - Good. I'm so tired of the vancian system it's not even funny. I'm not sure the power system is a good replacement, but I'm willing to give it a shot.
NO MORE SPELL SCHOOLS - Neutral. I don't know enough about the new system to have any opinion here.
FOCUS ITEMS - Neutral- As per above. Not enough information.
SKILL SYSTEM REVAMP - Mixed. I like simplifying the skills so that there aren't so many of them (Athletics for Jump, Climb, and Swim for example). But I don't want the skill system as a mechanic to be simplified to the point where you hardly use them, and I fear that's the direction they're going in. I'd much rather see something more similar to Iron Heroes.
BASIC RACES CHANGES - Good. I've liked everything I've heard so far. I won't miss the Gnome at all.
RACIAL PANTHEONS GETTING THE BOOT - Indifferent. I've only rarely used the published pantheons anyway. I prefer my homebrewed systems of religions.
ELIMINATION OF PRESTIGE CLASSES - Good. I'd far rather they focused on making core classes fun to play all the way through the advancement table.
EFFORT TO BALANCE FEATS - Good. I haven't heard anything bad about it yet. I hope they have a lot of racial and class linked feats.
PARTY ROLES - DEFENDER, LEADER, ETC. - Mixed. I don't mind it if it's to help people, especially beginners, design strong party dynamics. I will be very annoyed, however, if each role is required for a party. I don't want party design to be put into a box.
POINTS OF LIGHT SETTING DESIGN - Good. I like what I've heard, and even if I didn't, I'd design my own anyway.
LACK OF BACKWARDS COMPATIBILITY - Neutral. I don't really care that much.