Not a shooter, but superliminal I think has a few levels that let you use portals to change your size, and there’s no limits on how many times you can do it, so you can shrink yourself to be microscopic to the point where you can fit inside a straw and it takes like a minute to walk to the end of the straw. Everything in the room is modeled to be quite detailed, so there’s also a chess board, and you can get on top of the rook piece and it’s like being on top of a castle.
Pretty fun puzzle game
Not so much a game recommendation but a platform, but if you don’t already have a Nintendo switch, it might suit your style.
It lets you suspend any game at whatever point by just going to the Home Screen. You can then put down the switch and leave it for days or even weeks at a time, and then you can just turn the switch back on and pick up exactly where you left off in like 5 seconds.
I’ve been playing heaps of the new Zelda game, whenever I get a spare moment, but also if Nintendo games aren’t your style, nowadays there’s quite a good library of other games for the switch now.
Obviously the suspend feature doesn’t work for multiplayer games though, and to be honest I’ve found multiplayer in general doesn’t work as well on switch as other platforms, but it really is great for quick sessions of single-player games.
Also being portable is a great bonus