I look for two things in a deity:
1) Access to interesting domains so that I can create a mechanically interesting character.
2) Has a philosophy and portfolio that seems interesting enoguh that I can imagine someone actually wanting to worship (or at least propituate) that deity.
Without two, I find it impossible to RP a cleric. I take my RL religion quite seriously. Even if the game religion is 'just a game' it needs to have a somewhat compelling philosophy. I would assume that my character, a cleric, takes his deity at least as seriously as I do mine. I need to be able to imagine why my character follows this deity, and why he feels the need to encourage others to follow this deity. Otherwise, the cleric ends up as a hit point bank and the RP is very trite.
The domains are a meta-gaming consideration, but if you can't do anything interesting, it's often hard to contribute in an interesting way to RP no matter how interesting your character is.