I have played many great games on the PC, still these two are the best:
Guild Wars
World of Tanks
Both of them are truly unique online experiences!
> Guild Wars was both an adventure and a fantastic competitive experience. The latter was really well made. The game had a 24h ongoing online tournament, for 8 player teams, called 'The Halls of Heroes'. Guild Wars also featured really challenging arena fighting with 4 player teams. Boost the competitive part with really nice adventures, guilds and cool challenges... and you have a winner! You could mix hundreds of skills to create unique and fantastic skill combos. I spent over 3000 hours on this masterpiece. Guild Wars is my number one game of all time!
> World of tanks brought me the greatest strategical and tactical challenges in my life. 15 vs 15, 15 min battles, skilled men in tanks fighting to the death! What more can you ask for? Grand campaigns, tough clan war battles vs skilled European clans, diplomacy and fun! 40000+ battles so far. Of course the game has some flaws regarding tank balance, and the company's urge to make more money. Sadly the developers made changes which made me loose some serious interest of the game. I retired from active 'daily' play in 2014.
I have made a list of games that felt fantastic when I played them. Even if some of these games can't compare graphically to the ones that are made today.
In random order:
Desperados III
Asheron's Call
The Half Life Series
Left for Dead
Counter-Strike Series
Tomb Raider (2013)
Rise of the Tomb Raider (2016)
Total War: Warhammer
Total War: Warhammer 2
Rome Total War
Orcs Must Die!
Shadow Tactics: Blades of the Shogun
Team Fortress 2
Skyrim
Sid Meiers Civilization V
Dota 2
Warcraft 3
Dead Space Series
Prince of Persia - Sands of Time
The Bioshock Series
Doom (2016)
Plants vs. Zombies Series
Sky Force 2014 (Ipad&Android)
And of course online play at sites like Tribal Wars and Conquerclub!
Impossible Mission (Commondore 64)
M.U.L.E (Commondore 64)
Calefornia Games (Amiga)
Dungeon Master (Amiga)
Paradroid (Amiga)
Speedball 1&2 (Amiga)