1) I don’t like clerics.  I don’t like how they don’t fit any particular fantasy niche, with their armor and their weapons and their healing and their turning undead and their magic spells, I mean, it’s a grab bag.  It’s like a character who can use any kind of bow, also they have a poison touch, and can talk to fish, and that’s a base character class.  I don’t like how clerics have all these self-buffs and little bonuses that exist solely to bribe players into willingly taking on the role of medic.  I don’t like how clerics bring religion and the divine into the forefront (I don’t like how religion is handled in 90% of D&D settings; most of the time it’s like someone took Jack Kirby’s New Gods and got rid of all the good parts).  I don’t like how their healing ability is so crucial and so exceptional that playing without a cleric PC (or a near-analog, like a druid or a favored soul) requires the whole party to work around the hole.

2) I don’t like how insanely flexible high-level spellcasters get, how they can pull anything out of their pocket.  There’s a spell for every occasion, and it’s a spell a wizard can seek out and learn or, worse, a spell a cleric can just announce they have.  Every new supplement with additional spells increases the flexibility of the casters, and eventually it becomes tricky to impossible to keep track of (at least, that’s been my experience running 3.5).

3) I don’t like how limited in their options non-casters become.

4) I don’t like the huge disparity between the effectiveness of an optimized character and an unoptimized character.  I once ran a 3.5 game, there were two melee combatants, and one had about +5 to hit, +15 to damage, forty hit points, and better AC and saves than the other.

And neither of them were happy, because the overpowered guy, who was just doing what he found fun in creating an optimal and effective character, found himself bored with making full attacks over and over again, with no decision-making, instead of playing a caster and having some choices.

5) I find encounter design — making a group of monsters that are going be a challenge for my PCs — five thousand times harder in 3.5 than 4e.  It was incredibly easy for me to overshoot, and have to quietly ratchet down the monsters after the first round of combat made it clear that would be necessary if I wanted there to be a third round of combat… or, much more often, a combat encounter I spent an hour or two putting together, because there were all these needlessly labor-intensive steps, would get breezed through in a single round leaving me with nothing prepped for the rest of the night.

6) See #5, but with regards to treasure.  Working out what loot the party should get, what was appropriate for who and so on, was incredibly painful.  3.5’s tools were terrible for this, compared to 4e.

There’s all kinds of other complaints people make about 3.5, but these are what bother me.  4e fixed all of these specific problems — 1-3 by fundamentally rewriting how classes and spells and “powers” work; 4 by rolling back the menu of choices (though now that it’s 2011 that’s pretty well undone) and 5-6 by actually creating a bunch of robust tools that work well for me.  And by tools I don’t mean the DDI computer programs, I mean procedural rules and tables and charts and stuff.

But — as I grow more disenchanted with 4e — I realize none of these things need to be dealbreakers.  5&6, well, there’s a crazy-robust library of adventures premade out there.  1-4 can be dealt with by a) talking people out of playing clerics and b) everybody working together to ensure that people have characters in the same band of effectiveness and flexibility.  I’m told Pathfinder is better at that.