I read the title and got halfway through the first lil paragraph and the word “Portal” immediately popped into my head lol.
Otherwise, I think Titanfall 2 has the perfect FPS campaign. Just like Portal, it’s fun, replayable, fat free, and every level is exciting and finds a way to surprise you. The story is far from original but it’s told so well because of the fact that it’s an interactive video game and the two main characters are supposed to be the player and a robot so their relationship is defined essentially like the player’s relationship to the game. It’s not as approachable as Portal since the controls have more depth and complexity, but that’s why I said it’s the perfect FPS campaign.