Me, I'm just plain lazy rather than picky. Oftentimes, unless I'm absolutely and completely enthralled by a series, I'll let it linger in my watchlist with days, weeks, even months between episodes.
Action is nice, but what really does it for me is the writing. Hell, the premise could be the most inane thing in the entire world, but so long as the dialogue is interesting and the episodes imaginative, I'll be hooked till the very end.
Elusive as it is, authentic voice acting is also a great luxury. English dubbing's gotten a lot better over the last ten years, but the two standouts in my mind are Haganai and Panty and Stocking. Both of those shows had characters that talked like native English speakers; complete with idioms, slang, and plenty of swearing.