I start to appreciate games that implement complex and sometimes rarely noticeable (immersive, boo) mechanics that come off naturally. And I notice how a thought pattern behind bad ones could've progressed.

Bugs? My favs are buggy to the point some of these bugs became their own mechanics. I only get annoyed when the game bores me out, and if bugs can't make me feel like it, it's fine. And some better-done games are pretty boring to me.