As runequester said, clarity is important. A clean, uncluttered interface with easily-identifiable game elements is much preferable to a pretty but ornate and confusing one. Also, I prefer a distinctive and consistent style over general niceness of graphics, myself; a game should have its own look, even if it's not the best-rendered thing out there.
In any case, I value gameplay most; a game's graphics have to be pretty awful before I won't play it. But nice visuals certainly don't hurt.
