say what you will, but I will always have a soft spot for the Halo games. when it comes to dumb streamlined first-person shooters, Halo 1+2 are amongst the most enjoyable I have ever played. I'm not one bit interested in multiplayer though, so I'm not even gonna comment on that.
what I really like about them is the atmosphere, the color settings and the music. they've simply managed to make those games very pleasant to both the eyes and ears and they're good fun when you don't feel like using your brain while playing.