I like it a lot too! I don't know what this mix of 3D environments and 2D sprites is called (it reminds me of the first Doom), but I would like to know more about it. :) What engine is it made with? Is it Unity or something more specific?
I think the technical term is billboard, the game is made with Godot Engine, it's not made exclusively for making 2.5D games but it's quite easy to manage with
