https://imgur.com/a/n4wKWlT
There's some screenshots of what I'm seeing. I'm still able to walk around, jump, shoot the guards, and collect loot. Once I reach the last screen (with all the numbers and arrows) I can continue forward but the room will always look the same.
Huh, interesting. I haven't seen that at all. It's using the wrong tilesets but still the right room layouts.
I've actually just downloaded it from the site and tested it just now in retroarch with Mesen core and it was fine. Maybe try re-downloading it?
Sorry you're having that issue, and thanks for trying the game.