The people & the decision making are the most important. Good leadership is also of vital importance - one bad leader is enough to sink a team, especially at a startup.

I agree. There was one startup I worked for about two weeks. The boss keeps on asking me updates every once in a while and I had to stop coding just to explain to him what was going on with my work. It was frustrating coz I had to gain momentum/focus again. After two weeks I quit. I can't survive with that kind of work environment.

I think everything has to do with personality and it happened that my type didn't fit to that culture.