Hmm, lots of them but here's a try:

Civ-series

Football manager series (and Champ. manager before that)

Freelancer

Age of Wonders (all three games)

TES: Daggerfall

Europa universalis (different incarnations)

Everquest 1 and 2

WoW

Lotro

Vanguard

Problem with the MMO:s is that I have start/stopped many of them so maybe they don't count apart from EQ1.

FFXI - around 5 years but don't like abyssea so no longer play.

The Last Remnant - about 2 years.

WoW - 2 years but mainly played pre-tbc.

SOCOM 2 - 3 years.

And Oblivion 1 1/2 years.

Civ 4

Football Manager

Sim City

The Sims

Gran Turismo

Guitar Hero

FFXI

Someone mentioned Populous (not played for years but did play it for a long time)

---

Originally posted by Reizla

---

Originally posted by forest-nl

Skyrim PC

---

LIES!
Game is not even half a year old :p

---

Oh yeh i was not realy paying attention to title OP made i just sums up some games ive played alot my BAD sorry:)

For The Witcher 2 in my list.

About Skyrim ive played it so far 260 hours but stopped about 6 weeks ago.

Morrowind i think ive played over period of 6 months (2002)almost everyday and rest of year at least every week Skyrim is great but for me Morrowind is still by far my best in series.

I reply all the X-COM games over and over and most Final Fantasys. I played AvP2 online for a looong time, probably years.

My most weird experience with games i most loved is Metal gear solid i played the Japanse version becouse i could not wait so long for english version so i bought Japanese Import version. Could offcorse not understand one word but it was still awesome game experience on playstation 1 witch btw i also specially bought for that game.

The only game i keep going back to is guild wars. 

Played it from the start and still play it now, I dont know why i just enjoy it :-)

I've come back repeatedly to some older games.

Various "Total War" Games - Rome, Shogun 2, Medieval 2.  Depending on what setting I want to play and what mods that I install.  Between them, I definitely put alot of time with Rome Total War and the many great mods it had (has).

Sins of a Solar Empire - Great space strategy game in the RTS style.  Namely for the 2 mods, "Sins of a Galactic Empire" (Star Wars), and "Sacrifice of Angels 2" (Star Trek).

Company of Heroes - Still the true leader in RTS games, and dared to try new things.  Not some cheap, retextured, repackaged, regurgitation of an old game.  COH did things that other developers are still scared of trying when it came to RTS titles, and pulled it off extremely well.  The last great RTS game, IMO.  I also play with the Blitzkrieg mod and a voicepack so that German units speak German and not the terrible Hollywood German-English of the vanilla version.

Battlefield 2 - Still pop in time to time.  The last TRUE Battlefield game.  Fun infantry combat, large maps with varied terrain levels, vehicle combat, Commander mode, actual teamplay.  After BF2, only BF2142 comes closest to what BF is.  Not even the newer BF3 can even half-competently do it right like BF2 did.

ARMA 2 - Yes, it's a FPS, but it's a Mil-sim.  People afraid of the word "simulator" or a learning curve need not apply.  It's the franchise that tries to be what flight sims are for aviation games, but ground based, and particular emphasis in realism for infantry fighting.  BIG maps.  Unforgiving and strives for realism.  Mature community with no BS that you come across in other more popular FPS games.  I've repeatedly come back for trigger time in ARMA 2.

Falcon 4.0 - With mods, this 1998 game is STILL the best combat flight simulator out there.  It has received alot of good, serious loving over the years.  I still have the binder with the thick game manual, not the cheap PDF manual BS that developers do to give you less for your money these days.  The Dynamic Campaign System is a different experience every time.  Lots of factors affect the situation that you fly into next, and when flying, you can see and hear radio chatter that, hey, there is a *war* going on around you, and that you are really but one tiny game piece.  Dynamic Campaign Systems for me offer far better depth and variety in a campaign than any regular, scripted one can ever do.  It is also a flight sim from the Golden Era of these type of games, the 1990s.

Planetside

Star wars Galaxies

Dark age of Camelot

Everquest

Cnc Renegade 

TES3 Morrowind

smb 1-3

super mario world

old castlevanias specifically 1 and 4 but they all fun

megaman all of them

Alot more tbh but theres some all time favorites.

honorable mentions - LOTR battle for middle earth 1 and 2 (PC version), and Empire at War and Forces of Corruption.

Final Fantasy XI: Not my first, second, or even third MMORPG, but the only one I've ever enjoyed enough to sub for 2 consecutive years straight.

Saints Row 2: The series that ruined Grand Theft Auto for me. Third Street 4 Life!

Ace Combat 6: By far and wide my favorite game on XBox 360.

Mega Man 2: IMO the best game of all the MegaMan series'.

Paperboy 2: Simple...weird...fun.

Rampage: The original, not the craptastic remakes that came out on the PS1.

Dragon Force: No, not the band. The awesomeness that graced the Sega Saturn way back when. A game in my collection that I never plan to part with

Originally posted by FrostWyrm

Dragon Force: No, not the band. The awesomeness that graced the Sega Saturn way back when. A game in my collection that I never plan to part with

I had that game on my 'ol Saturn.  It was quite a nice game.

Guardian Heroes on Saturn is also an AWESOME game!

Hmm some of the games I have spent the most time on are

Sacrifice - PC, came back to playthrough a couple times through the years since my first run at it :)

Masters of Orion 2 - PC

Age of Empires 1&2 - PC

Ogre Battle - SNES

Earthbound - SNES

Final Fantasy III - SNES

Final Fantasy Tactics - PS

Monster Rancher - PS went through every CD I could find for a critter :D

Super Smash Brothers - with friends

SWG

Zentia - dodge and block in combat!, great guild, burned out...

SC 1 and 2, though i played 1 for like 5 years and SC2 hasn't been out that long.

WoW, started at launch, didn't quit until right before firelands, just resubbed for a month see DS, will probably check back at expansion.

Fallout 1-2,Planescape Torment: I replay all 3 of these probably once a year, i played through all of them after quiting FF 13 because it was so horrible i had to be reminded of what a good rpg was.

Dragon Quest 9: Because it's like an mmo that makes me nostalgic.

Good topic!

For me:

• Civ series (alternate between 4 and 5)
• Alpha Centauri
• Pirates!
• TF2 (old and new)
• EvE (game I keep coming back too)
• Panzer General I (even on easy, game is hard!)
• SimCity 4

Ultima online FTW!!!!

The games that have kept me coming back for more, or in one's case, never leaving-

Dungeons & Dragons Online - Been rocking out here for six years and counting.  Will probably be here until they turn out the lights or do something incredibly stupid (the latter being entirely possible with Turbine)

City of Heroes/Villains - Played for three years straight and still pop in every few months to see whats new

Counter Strike - Yeah, still jump in for a few rounds of 1.6

Half-Life 2 - While I'm no longer doing the once a year run through, I'll still fire it up for an hour or two when the urge hits.

Final Fantasy 7 - With this being on the Playstation Network, I no longer have to fire up the PSOne to give it a spin.

I'm thinking myself pretty young when it comes down to this industry to be honest, but I still had my favourites.

Diablo 2:LOD - Loved it. Played through that as every character, several times. Specially worth the money as I got the game and the expansion for only £10!

Fable:The Lost Chapters - again, another love. Got me all hyped for the second just from having played the first. I was all about shelling out a silly amount of money for all the extras, collectors edition etc... turned out to not be worth it. The first still sticks with me.

Warcraft 3: Reign of Chaos & The Frozen Throne - my first RTS! oh the memories! And that map editor? I've found non that can match it.

Runescape - I'm not even embaressed to say, I spent so many hours playing this, returning time and time again, it's just silly.

Can't think of any others off the top of my head... so they must be the ones that made the most impact...

actually looks like a weird list to me now...

dynasty warriors series (fun hack n slash)

civ series

total war series

mount and blade (withs mods)

pokemon games (can never get to old to play pokemon)

Any "Good" Post and Including Street Fighter 2 2D Fighting Game - I'm a pretty avid fighting game play and I tend to play older ones from time to time.  They never get old and most have solid mechanics to this day.

Good Turn Based Strategy (X-COM, Jagged Alliance, Fire Emblem, Tactics games) - Very fun games to come back to.  Get tons of enjoyment out of them.

RPGs - There are plenty to come back to from older titles like Bard's Tale and Might and Magic, to SNES JRPGs, to PSX RPGs, to even more modern titles.

I also still play N64, Gamecube, and Xbox titles from time to time no matter what genre.  Mario 64 is one of the my favorite all time games for instance and I tend to revisit it.  Also a pretty big fan of Goldeneye 64.  Still, the 3 genres above are the ones I find easiest to come back to.