I've re-started a lot of games just moments after finishing one playthrough because I like playing through with different classes and am obsessed with dialogue. Just played through The Witcher twice in a row and have played endless permutations of the Dragon Age games,Skyrim, Diablo II, Sid Meier's Pirates, Caesar III, Neverwinter Nights, both Baldur's Gates, the Dungeon Siege games... When I play a game, I ususally invest hundreds of hours in it before moving on. So I can't even imagine having over 500 games!

Diablo 2

If I have finished a game, I hardly ever get a desire to start it all over again right there and then. I might think that maybe I should e.g. try it again with some other character some time later, e.g. Nox or Diablo 2 with a different class.

Certainly there are games which I have finished several times, sometimes months or even years between the replays. A couple of months ago I replayed the Starcraft campaigns (I've finished that game probably dozens of times), and quite often I get an urge to re-install the first Age of Empires and start playing it (but then I keep reminding myself that I've also owned AoE3 for so long without ever playing it, so I really should try it instead...).

Then there are games which I've finished only once, but from time to time I keep thinking how nice it would be to install and replay it from the scratch again, you just have so good memories playing it before. One such game is Far Cry 2. I'd just love to jump into a jeep again and drive through the whole map, with the scenery changing from a jungle to savannah to desert, snipe baddies from a hilltop, scorch everything with a flamethrower etc. So romantisch!

But like with AoE games, I keep reminding myself that instead I should really start some new (action) game, like playing the Crysis series, Stalker series, Darksiders series, Mafia 1-2, GTA IV etc...

Some RPGs mainly, because I felt I made some bad decisions either in character creation, or later in the game. Like:

Baldur's Gate: I restarted it several time from a scratch, sometimes because I felt maybe I could have a better character, but sometimes simply because I hadn't played the game for quite some time that I had forgotten what I was doing in the game and where I was going when I left the game. So I restarted the game "more organized", keeping a log myself which subquests I've already finished etc.

Fallout Tactics: Quite late in the game I learned I had made some choices that were anything but optimal. I restarted it from scratch when I had only few missions left, and yes it did make a difference, my new party grew considerably stronger as I made better decisions in developing them.

Dungeon Siege: Legends of Aranna: I restarted both the base game and the expansion. The base game I restarted because I felt I incorrectly tried to make my characters "jacks of all trades", when the game actually favors strongly specialized characters that concentrate on doing one thing good.

The expansion pack I restarted because at first I didn't understand fully what the "item sets" were all about, and I had foolishly sold some such special items, unable to recover them later (it seems that if you sell some item to a storekeeper, that item will vanish for good after awhile; so it isn't like Fallout 1-2 where the storekeepers seem to keep everything you've sold them for the rest of the game).

It wasn't a game-breaking thing that I was missing some such special items, but I just wanted to see how well such item sets work together when you find all the pieces. Some of the item sets were quite useful and powerful.