Neverwinter Nights, including SoU and HotU. This occupied my early gaming years. I made so, so many characters, and I will forever miss the masses of multiplayer servers and RP availability, and the community made content. That thing got me through secondary school sane. (Has been and always will be a geek)
Sins of a Solar Empire. Don't you dare rip on one of the VERY FEW games that are literally holding up the entire space RTS genre. With Homeworld 2 being as old as it is (Not saying that's a bad thing) People tend to look for newer games. I know of three. Galactic Civ (Which is technically TBS) Haegemonia: Legions of Iron (Which came down to who can buy the most battleships fastest, and how do you pronounce it anyway?) And Sins of a Solar Empire. Granted.. it has no campaign. I will cede that point. But show me ONE game that is a better space RTS than Sins.
Mass Effect 1/2. Granted, there are little niggles. But... Mordin. Nuff said. Argument, invalid.
And above all else because it pretty much started my geekdom, was my childhood hero, and my first console/console game, and got me into gaming... Sonic 1, 2, 3 & Knuckles for the Sega Megadrive.
C'mon, say it with me... "Seeeegaaaaaa."