I haven't got a lot to say that hasn't already been said, but damn the pump-action feels satisfying. I've always loved games that do the "click again to pump" thing on shotguns. (Well, I've only ever seen it in doom mods, but still!)
I also appreciate the little bit of lore at the start of level 1. The idea of a gang that's using reality-bending to its advantage is fun, and the phrasing of "Kill these 3 targets and you will gain access to the light" is delightfully ominous. Someone else compared the levels to EYE already, but that bit of implied storytelling is what really gave me EYE vibes--or maybe a bit of Cruelty Squad.
I agree with Zackarotto in that it'd be cool to have a bit of stealth, with enemies not immediately recognizing when one of their number has been possessed. If you really wanted to, you could probably build an entire immersive sim around that mechanic.