If you want a humorous FPS and have $2.99 to spare you can’t really get any better than Giants: Citizen Kabuto. It’s 50% off right now as part of an Interplay promotion at GOG.
It’s an old game, released back in the dawn of time (or the year 2000, whichever came first) but it holds up well. There’s very funny dialogue, the graphics were amazing for their time and still look great. Back then you’d be hard pressed to find a machine that could play it well but that’s not a problem with any sort of modern machine.
Go on, go on, go on. It’s lots of fun and I can’t recommend it enough.