Battlefield 2. This is the game that made me upgrade my computer back in the day (and it still was barely enough).
Now, a few years later, and a few expansions later, and they are doing a great move: making all the expansions free.
The bane of any multiplayer game is a splintered community that makes it harder to find a compatible game. Requiring DLC to get on a specific server to play with certain people limits the number of players willing to continue paying for this product, instead of simply moving on to the next, better FPS.
But now they are reforming their community, with a game that will now run on any modern system.
I’m looking forward to when it is released: