I have a ridiculously long list but here are a couple of the most relevant,
Steambot Chronicles: Sandbox game in the vein of GTA, but features a tank based combat system and industrial revolution setting.
Space Station Silicon Valley: Platformer based around a computer chip that can inhabit robotic animals to use their abilities, classic blend of sadistic humor and cutesy graphics, sadly the version of the game that shipped is bugged.(You can play all the levels and get all but 2 collectibles, but not the secret ending)
Shadow Man: Best voice acting in any video game period. Like other action adventure titles (zelda, okami) you get to revisit areas after you find new powers. Has fitting enemies for its underworld setting, such as the demonic rottweilers and slasher villain demon. However I can't actually recommend it because it has two problems.It's sometimes confusing. (To use zip lines you must manually unequip both left and right hands) ( Doors that are actually full fledged physics objects that you have to jump onto the handle to pull down) (Ambidextrous gunplay). It is a very long game, and contains some nasty platforming areas (remember the instant death pits with no nearby checkpoint on the second to last leg of Half Life 1? Multiply that by twelve). It is actually obtainable today via both Steam and GoG. But you absolutely must print out the overworld map that ships with game. It is a necessity. Is it really underrated if it's a niche title for hardcore people? Yes, Dota 2 has 4 million players when its clearly designed specifically for the MOBA audience.