I don't know how many times I have replayed through Diablo 2. I can say without a doubt I have more hours logged on that game then any other game for the PC.
Why? Had a lot of friends that played it and I loved trying to always find better gear and get your guy decked out.
I have put in many hours on a lot of fighting games too. I don't know if I can call it replaying, as they are all vs matches

. But several of the Street Fighters (Most Alpha 3 & and #4 for the PS3), Super Smash (64,GC & Wii), SNK vs Capcom 2, several of the Guilty Gear games(Mostly X & X2), several of the Naruto games, and most recently Skull Girls

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Why?Best friend and I like the "Street Fighter Style" fighting games (ei, not all pre-programed combos like the Mortal Kombats). You don't have to dump a lot of time in them, and are fun to play casually. Matches are quick so if you have more people than controllers its easy to cycle through everyone.
Also same story with shooting games. Played the hell out of Perfect Dark on the 64 back in the day. Also played co-op on Resistance 1 & 2 quite a bit. Really had fun with Red Faction #1, and being able to blow up almost everything

. Never have been much of a Halo guy tho. Why these shooter games? For me so many shooters are the same game over and over, just different skins put on them. A shooter has to have something that really grabs me. Perfect Dark it was the Simulants in multiplier mode. You didn't just have to shoot your friends any more! Resistance was the fun weapons. And Red Faction #1 was the ability to blow up most of the environment.
Back on the PC I have played Sims1 & 3 a lot, SimCity 3000 & 4000, Civ 3,4&5, Sid Meier's Railroads, Railroad Tycoon 3, Age of Empires 2, and Age of Mythology. Again games that I don't know if you can say "Replayed" because for most there isn't really a story line to replay. But many hours spent on all of them.
Also used to be a WoW addict.

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As for my Why on the Sims games? I don't really know. I acutally have more fun building the houses and then playing in "Live" mode

. SimCity, Railroads, & Railroad Tycoon - I like trying to make lost of money

. Civ, AoE & AoM I like "Command & Conquer" Style games, and like conquering everyone else - which is much harder to do in the Civ games

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Wow was because I had a lot of friends playing it, then made new friends. I had loads of fun while playing with all my friends. Now they don't play so much and I got board.....