Personally I think it's high time monsters started working a lot more like classes and a lot less like stop-gap challenges.

They also need to start acting as part of the world, rather than reclusive things that only emerge when the PC's are around.
I've got no problem with monsters that you can use smart tactics to overcome...the ultimate purpose of a monster is to expend party rescources, be it reviving the barbarian or helping out the halflnig who couldn't fly.
What gets me is paper tigers (mindflayer! pretty much any fey!), melee monsters (Yes, I have seven attacks on a full attack, plus rend and pounce, why do you ask?), and undead (sooooooo many....sooooo few hp!).
By "acting more like classes," I think monsters should get more features with their HD than just hp, and that 1 monster HD should approximate 1 PC HD, and everything that comes with it. I think that the powers of monsters should be tied to HD and advancement, so that a mind flayer out of the box may not have very many powers, but as you give it HD and advance it, it explodes with psionic goo (dness).
But now I'm giving away inspiration for things I should be writing. Heh. If I get my way, you'll be seeing better monsters in the future.