I'm not into the scene as much as you guys but here's my own take.
Character design - I tends to leans towards those character design in Anime like Gundam 0080 & Black Lagoon. Carries more emotion expressions.
Storyline/Plot: I guessed for most of us, a decent storyline/plot is quite essential considering most anime carries more than 6 episodes and you dun wanna watch all of it and end up without a clue.
Besides these two points, I oso look into the illustrative direction... background scenes and such. The use of 3D form (esp in Mecha).. whether issit relevant or blends well with the rest of the scenes. Can't help it cos I'm a very visual person.