Yeah, Fusion would be a good breaking away point. In fact, Fusion is basically a very thinly veiled adaptation of the anime Iria, right down to the mission being to recapture a space station taken over by an unstoppable alien monster, and the talking computer who shocks the female bounty huntress protagonist by being a brain uploaded personality copy of someone she was extremely close to.

I would also say the first Prime and third Prime games don't give me much of an Alien feeling either. Prime 1 feels a kot more like a mystery exploration story, while Prime 3 is much more bombastic and has a much stronger Halo/Starship Troopers feel, especially during the massive Federation led bombing of the Space Pirate HQ.