I consider myself a fan of 4e and a critic of its flaws. It's the system I am currently running, and it's one of those things where I'm constantly getting better at approximating my gaming ideal with it.
That said:
- For me, probably the single best feature of 4e is monster and encounter design.
GOD, YES. 4e monster design is SOOOOO SWEET. (See the Monster Project link in my sig if you want access to a metric buttload of monsters that I've converted.)
4e's strength isn't in the rules per se; it's how sweet and tight the math behind the rules is. Unfortunately, that's also its weakness- there are so many assumptions baked in that you really can't get away from without bending the game pretty hard, things like treasure values/magic item wealth (at least weapon/implement, armor and neck items)... certain feat taxes are
close to obligatory... a certain level of stat optimization is almost required... and so on.
One of 4e's other key strengths is how strongly it promotes teamwork and group play. Unfortunately, this is a potential weakness too, since it shoehorns some groups into a certain type of "Who's playing the leader this time?" mindset, which has the illusion of limiting choice, and it also makes smaller-than-four-person groups less effective against an equivalent encounter than a four-or-more person group (i.e. a party of 3 has a tougher time against 3 standard monsters than a party of 4 vs. 4 standard monsters).
I do like action points; they're a lot of fun and get better as you hit paragon level. (I know that Eberron had 'em in 3e, but 4e made them quite mainstream.)
I
loathe the incredible amount of tracking involved in combat, especially once you hit the higher levels. Also the exxxxtreme option overload in having thousands of feats and powers to choose from; I'm with delericho in that a system that has the same strong need for e-support as 4e will lose my interest. (I do recognize that it's not all option overload making this an issue, some of it is the amount of math and all the stuff you gotta write down in order to make a complete character sheet by hand- I firmly want a system where blank paper and pencil are all you need to make a complete character sheet, where you do not need a worksheet to figure out your bonuses.)
I'm of mixed mind about healing in 4e; I really like surges but I really hate that there is no way to ever require weeks of rest of recover from serious wounds.
4e's magic items are great in basic conception but only so-so in execution. Too many are kind of boring. But there are tons of gems out there, once you excuse the "necessary for the math" bits on offense/defense items.
Another of the things that 4e does really well is encounters, especially combat encounters. This focus on the encounter is kind of limiting, though, because of the need to balance the encounters against the party; again, strength and weakness at once, thank you tight math.
I know I'm one of the only ones, but I'm a huge fan of skill challenges. Strong conception, weak presentation. However, I've tried hard to get to know the potential of the skill challenge system and I've learned to tweak it substantially. Sometimes there's no "Fail the challenge on 3 failures"; sometimes it's "How many successes can you get in x rounds?"; sometimes it's "the number of successes before 3 failures determines how long it takes to travel across this inhospitable wilderness"; and so on. The system as it is presented tells you to do this, but most of the published examples in books and modules are terrible. SPOILERS for Keep on the Shadowfell: [sblock]KotS's example of a skill challenge when you meet the undead knight is particularly egregious- he basically asks your party for someone to show their Arcana skill and so forth.[/sblock] Change the presentation and make it something that makes sense and you're better off. Also, I rarely tell the party that they're in a skill challenge, though they often figure it out.