I've got a lot of favorite games, so I'll use my favorite arcade game, Mappy. I don't really like the bonus stages, I feel really rushed when I play them. They're fun, but when I first played them I always lost because I'd move too early and end up breaking the trampolines and losing.
I love Halo and I do agree with you on the flood. They used to freak me out when I was a lot younger, but now I'm pretty used to them and just kind of slash through them.