Hmm, well there are a lot of factors that go into good anime, but I guess to get me to watch it it has to have a minimum of:
Good/interesting characters– If I don't like or don't care about who the story's about, why am I watching it? At the very least I have to be intrigued by them.
Interesting/intriguing plot-- Having good characters is a good first step, but if I don't like or don't care about the plot, then there's not much point in sticking around to watch them, is there?
Anything else I can deal with, be it sub-par animation, less than striking music, mundane locales, etc. Sure, I like action but it's not absolutely necessary for me to be able to enjoy something, and the same goes for romance or even humor, come to that. As long as it's well-done, with good, solid characters and something interesting for them to be doing, I'll probably watch it.