Monster games?
 

Because playing as a puny human can only interest somone for so long, I am calling upon all NPFers to share their knowledge of games that allow the player to play as, beasts, monsters, and critters of every description. Suggestions for any gaming platform would be helpful, and could include any genre. Mods that add this effect to the game would also be much appreciated!

Shin Megami Tensei is your ticket...if you are into RPGs. However, it may be a bit late, and rather expensive, to get into the series. I just re-bought SMT: Nocturne with the strat guide for $80 bucks over at eBay (which is, truth be told, about what I payed for both when it first came out a few years back). SMT: Digital Devil Saga might be a bit cheaper, but I hear it is still hard to find. If you're planning ahead, Persona 3 comes out August 14, so you have time to pre-order.

Well... Overlord. Sort of.

You're still a beefy guy in heavy armour... but the real stars are the Minions you contol as the Overlord.

What the heck is the one called where you are the hand and you build a dungeon. They made 2 of them, I think it was PC only. Dungeon Keeper maybe?

Darkness in Multiplayer you can play as a darkling! enjoy riping the heads of of humans!

Oh, in the tone of Doc's post, Alien vs Predator is a most excellent choice.

Stubbs the Zombie. You play as the undead.

Rampage: World Tour (N64) was an excellent adaptation of the popular arcade game.

Okami is probably last year's best game so I'll definitely suggest that, I'll also second Shin Megami Tensei : Nocturne, both are for the PS2. And yes Dungeon Keeper is what you're thinking of Demetrius, damn that was a fun game.

I think it was Dungeon Master. But I only saw my friend playing the game once so its not exactly accurate. But I'm fairly sure it was made by Bullfrog games.