Easy answer is E.Y.E: Divine Cybermancy.

It's a janky mess built on the source engine. The plot is downright incomprehensible. Gameplay mechanics aren't properly taught to the player, leaving you to work out how everything works (my legs are ok). The maps vary massively in terms of quality (the tutorial area for example has an optional side path that is just an incredibly long empty corridor that takes, like, twice as long to cross than the path you're railroaded towards to reach the same destination). It's basically an unlicensed WH40K game so it's got my dislike of Warhammer to work against to win me over.

Despite this, I have a huge soft spot for the game. It's one of the comfort games I boot up and play when I'm sick and sad.