they are not just all about killing and shooting games, there are such games for them but there is also a huge range of games that are not about killinig and shooting (I play golf on mine quite a lot)
They work through a normal TV set and generally have nothing to do with your computer at all, and Xbox's do not have a blu-ray drive, it's just a normal DVD drive in them, though they do make a pretty good DVD player (it's what I use as my main DVD player)
If your going to get one go for the version with a hard drive (the 20gb hard drive is adequate for most)