Ok, so recently I finished Boltgun and its DLC. It's like an old-school shooter, but you play as a space marine. I picked it up ages ago on sale, and it was finally time to give it a spin.
I used to paint Ultramarines when I was a kid and have always had a soft spot for the Warhammer universe (recently replayed the Dawn of War series too, excellent Warhammer 40k RTS), so this was a no-brainer.
I liked the aesthetic and the graphics, and also the combat was pretty satisfying, you can do in-air chainsword kills and fun stuff like that.

Negatives
I can't say I have any huge negs, but there were a few things.
I thought the weapon selection in the main game was a bit sparse, with some things like the bazooka missing (it was added in the DLC tho). I also felt like I would often run short on ammo for the juicier guns.
I think they could have added some DLC with other factions, maybe some orcs or something, you know, some variety in who is being killed. It might have been fun to have a mode where you play as chaos too, flip the script a bit.
The difficulty on normal was fine, apart from the boss fights. I found them super hectic, way too many enemy spawns, not enough ammo, and bullet sponge bosses. I felt the arenas were quite awkward too, like i'd be falling off platforms and things like that.
They have an invincibility and gun/ammo cheat inbult in the menu and I'm not ashmened to say I used the shit out of it!
Positives
All over tight controls and mindless, killing gameplay. Not a bad way to distract oneself from the depressing reality of fiat land.
If you are getting close to an age where you will soon need regular prostate exams, you might like it more.
In terms of classic FPS, most people like Doom or Quake the most, but Duke Nukem was one of the main games I played in my teens. I think I liked it so much because it was set in our world and not in a literal hellscape.
The maps in Boltgun were the latter, space/hell variety, and a bit confusing, but there is an in-built navigation system which made it easy to manage.

All in all, if you are looking for an old-school type shooter that is fun, this is a good pickup, even if you are unfamiliar with any 40k lore.