I’ve been testing FPS mode for Alien Blitz, it’s quite fun
There are a few technical problems (viewing through walls, that kind of things), but nothing that can’t be fixed.
The major issue though is from a gameplay perspective: the game was not meant to be played first person, and it becomes a bit too hard.
In top view it is quite easy to doge bullets and missile, but in 3d it is a lot harder, and usually means player has to retreat instead of facing hoards of monsters.
So I don’t know if FPS mode will be a “complete” feature or just a fun mode to try… it will basically change level of completion from a technical point of view.