Feats are the only part of 3ed which I think there's never enough. There are still many areas of the core rules which are best served with feats than with base/prestige classes abilities.
For instance, any sort of specialization with armor (reducing ACP, reducing ASF, improving AC, improving movement, extra defense capabilities) is still not explored enough. Same thing with opening up new tactics or improvements to charge, grapple, overrun, bull rush...
Why feats are the best piece of rule for these IMO? Because feats are open to everyone (save a few exceptions). Prestige classes in theory are open to everyone, but in practice they're not. New base classes are even worse because require you to fit your character into a completely different advencement "railroad", or otherwise at least face multiclassing which is just unfeasible with caster classes.
What I don't like instead, is all those feats which give supernatural powers which basically just end up being a rehash of existing abilities.
Especially I dislike feats with half a page of rules, a feat should be as simple as 2-5 lines of description.
Furthermore, I'd like to see feats which don't always require Power Attack or Combat Expertise, but feats which you can take without needing other feats, or at least which require something different that these 2...
In short, there's too many unnecessary (and unnecessarily complicated) feats, and not enough basic feats.