In creating this list I realized I'm having to leave out a couple of individual games that would be on my Top 10 list because one game does not equal a franchise. I tried to think about it in terms of the amount of playtime I've given each as well as the truly memorable moments that come to mind.
1. Unreal
Unreal and Unreal Tournament are the two tops for me. The amount of time I've sunk into custom content alone is staggering. Both games were watershed experiences in their respective sub genres.
2. No One Lives Forever
Excellence in writing, set pieces, and gameplay. Though there are officially three in the series I recognize only the first two with those being so superior that it more than makes up for the third.
3. The Elder Scrolls
Still the king of open world action-RPGs. Immense, beautiful, and entertaining.
4. Half-Life
These games really raised the bar for singleplayer first person shooters. While I've grown to despise The Canal part of HL2, I can still power through it to soak up the immersive experience and rich world it offers.
5. Doom
Wolfenstein aside... this is why we have first person shooters. The levels are packed with secrets and I love the intense action. It's one of the first games I recall really drawing me in
with its sound. There's nothing like hearing a snort or growl coming from places unseen to get your pulse pounding.
6. Mario
This is a series in which each game just seems to get better and better. The critics always say "oh more of the same" but they're wrong. I'm always amazed at how a series spanning two and a half decades with each game filled with dozens upon dozens of levels can manage to deliver new things to do and see on such a regular basis. Sure themes are revisited but there's always something that makes you say - wow that's crazy. It's just pure fun and the gameplay is always spot-on, and the difficulty ramp is just about right for nearly everyone.
7. Total Annihilation/Supreme Commander
This was the RTS series that reeled me in to the genre. It's one of those games that gives you really cool toys to play with and then just gets out of your way. There's so much custom content for the series that it boggles the mind. I can always fire up these games and play for twenty minutes... or an hour... or two.
8. Star Wars
I love the franchise, but this one gets in more on volume than overall quality. There are some real clunkers if you listed them all out. But there's a bit of brilliance sprinkled throughout as well. Standouts for me include X-Wing vs. Tie Fighter, Dark Forces, Jedi Knight, Rogue Squadron, Knights of the Old Republic, Republic Commando, and even LEGO Star Wars. Add them up and that's quite a lot of great SW moments.
9. Street Fighter
Like most, the second installment really got me hooked. I recall massive events that would take place in arcades when the game was released. You could just go and watch people play for hours and it was one of the first arcade games I recall having a second monitor set atop the cabinet just for spectators. I sunk thousands of hours into the series with standouts for me being SSF2:Turbo on SNES, GBA, and 3DO. Street Fighter 4 got me back into the series and it's a game I can pick up and play at any time.
10. Serious Sam
The Second Encounter is almost worth the price of admission to the series alone. The humor, the crazy secrets, zany gameplay, and wild weapons all come together to make near FPS perfection. Plus... in how many games can you find a secret area that allows you to find a miniature movie set featuring you in the finale of the previous game? And lets you zoom in on yourself with your sniper rifle and kill yourself in the current game by killing yourself in the past?
Awesomeness.
Nearly made it:
The Legend of Zelda
Castlevania
Portal
Diablo
SimCity
BioShock
Metroid
Sonic the Hedgehog
Age of Empires
Final Fantasy
Not my personal favorites, but worth mentioning:
StarCraft
The Sims
Grand Theft Auto