As realistic as possible. I also like dark atmospheres for my shooters. Gears of war 1 was PERFECT. it nailed the gritty dark atmosphere perfectly

Weren't games meant to be an escape from reality? Now that so many people want it super realistic... *shrug*

So visual style preference goes with game genre preference, to a large degree.

It's probably easier for me to say what I like the least rather than the most. For me realism is probably my least preferred up to now because it can never look really real, so there is always a slight let down, even though a game may be the most realistic looking game ever (so far).

I don't think I have a favorite style really.  Here's my favorite looking games to date:

TF2's style is just so clean and awesome.  I love it.

I don't think I need to say anything for this one.

Realism can look awesome when it's done right.  Plus, the tropical setting helps.

This is just a perfect mix of everything for me.  It's pretty close to reality, but the world still remains uinque and seperate from ours thanks to the cool style and lighting.

Hand-drawn unique awesomeness.  Odin sphere looks amazing.

I don't dislike any graphical style but my favorite is a CGI anaimation look. Rachet and Clank is the closet a game has come to playing a Pixar movie and is one of my favorites this generation. Hopefully the follow up will surpass it.

everything looks great. That's why styles exist.

My favorite,... hmmm I really really like CGI, or stylized like Gears. Realism is awesome too, as in MGS series.
Superflat (cel-shaded) was also grand in Jet set radio, and looks great in PoP.

Anything done well in 16-bit or 32 2D. Sword of Mana was a decent game but the sprite work is beautiful.