Powerslave did one thing better than all other Build engine games: platforming does not suck. In fact the entire game revolves around it, rather than an FPS it's one large environmental puzzle first and foremost. It's a bit of a shame it went under the radar to be honest, it's on par with the big three for the most part. Nice meaty weapons, an actually useable flame thrower. Bullets go where you aim. Good stuff.
Except the levels... there is only so much you can do with an Egyptian theme
Eventually it gets quite samey, but the platforming and the many traps help to keep the grind away.