Alien Breed (original) gets my thumbs up!
The original Alien Breed still has the best Aliens feel to it, you really feel like you're in a space station with aliens around each bend. The music, awesome. Graphics, superb. Too easy? Well I've played this game a lot and never finished it so either I'm not particularly good at this game or it's not as easy as people claim. All the others in the series were good but lost that feel, they felt more like your standard platform run-around-and-shoot-things affair. Alien Breed 3D was OK but a bit chunky. I would still rather play the original than any of the others to this day! Thumbs up to Team 17 anyway for a superb Amiga series!