: The alien weapons don't feel alien at all in most cases.

Pretty much this. The last time that the Covenant armory felt truly alien was Halo:CE.Aaaand you all know my opinion on the Forerunner weapons. =(

I think it was a mistake to introduce so many UNSC-equivalent weapons in Halo 2, and this situation wasn't fully rectified with Reach. If I'd had my druthers, I would prefer the Concussion Rifle to be merged with the Plasma Launcher so there's no straight equivalent with the Grenade Launcher and the Spartan Laser. The DMR would be replaced with the Battle Rifle to make the difference in precision weapons even greater.