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

Rat maps! Those were so fun back in the day. Some real good ones for CS and HL1.

There’s a survival game called Grounded that’s basically this but even smaller. And a coop story action/adventure called It Takes Two that does the same.

It Takes Two is a great co-op (no singleplayer) game where you play two parents who are going to a divorce when they are turned into two dolls and need to find their way to their daughter while getting across their yard and house.

It's really fun for couch co-op!

Good old de_rats. I never saw something like that for other games, but brings up memories. I should install 1.6 again sometime...

Man, this post brought me back memories of Unreal Tournament (and 2k4) and now I feel very nostalgic for all those custom maps and weapons. Used to spend so much time playing giant insta-gib deathmatches (and when I had all the time in my late-teens/early 20s). Wish that game is still supported.

There's a freeware (open source but copyrighted art) shooter called World of Padman, that's pretty much what you're describing.

EDIT: You wanted "modern" but, it's slightly less so. Sorry.

Like the Duke Burger level in Duke Nukem Forever?

My kids showed me some Minecraft maps with that concept. Unfortunately I don't know where they got them.

In the Thief: The Dark Project mission The Sword you can find a gigantic room.

You reminded me of Toy Commander for that sort of map design. Lots of memories of it on Dreamcast.

I love(d) them, too!

Maybe check out Tinykin, it's great!

I loved these.

I also loved Sarge's Heroes for the N64 for kind of the same reason.

I love being tiny.

This reminded me of the bedroom level of Twisted Metal 4. Loved driving around that map. Felt like I was a hotwheels car.

It's not a new game, but Chibi robo is entirely this concept

Enemy Territory had an awesome one called Cortex! Should download it again

Did anyone else ever play Airfix Dogfighter? You got to fly model planes all through a house and break glass and stuff. Super fun times 😁

I haven’t actually played it yet, but HYPERCHARGE: Unboxed has been in my Steam library for ages. That looks like it may scratch your itch …

I really miss some “toy soliders” 3D shoot-em-up that I can just baaaaaaarely remember from the 1990s … does anybody remember the game I’m thinking about? (There was definitely a series, I distinctly recall the name ending in “2” …)

Theres hypercharged: unboxed its oretty fun. Also some toy story games kinda scratch that itch for me

Supraland is also a good game

Grounded comes to mind

Haven’t seen this concept for a while. I remember playing shit out of Airfix Dogfighter, where you were basically controlling a plane model from WW2 and fighting around the house with other planes. Great game

Ah yes, good old ttt_teenroom.

Those maps make callouts very easy because pretty much everything has a name already, so you don't need to argue about what's what.

TF2 has some good ones. Those were the days, along with the original prop hunt, rocket jump maps and sledding.

HL2DM had some awesome rat maps. I need to backup my collection of source maps off my old hard drive.

Elite Force 2 Quarterdeck was fun.

It's almost a decade old now, but I enjoyed playing Catlateral Damage back in the day.