I put a solid 300-400 hours in to Morrowind. The only reason I didn't do more was because I bought it for the Xbox (my computer at the time sucked) and couldn't download any mods. All the same,I managed to make my own fun throughout the game.
Oblivion, on the other hand, earned me a solid 500+ hours of playing. I got it a few weeks after it came out, for the PC, and after playing through it once I modded the hell out of it and played it through another three or four times, plus a few saves that I never even got past Kvatch but put quite a few hours in to testing out mods and doing awesome shit.
For whatever reason Fallout 3 never caught my interest like the other two did. Probably an effect of the barren environment; I really enjoyed the foresty-ruiny-whatever in Oblivion, and the wasteland that is Fallout got incredibly gray and boring after a while. I did a bunch of exploring and such, but honestly never finished that game.
I'm sure I've put at least a thousand hours in to playing Red Alert 2 since it came out. I still play a couple games of it, and me and my friends will get on RA2 sprees where we'll just play three or four long games of it in a row; we'll build up our defenses until the bots can't even think of getting through, then build up our armies until we can just roll through the bots, then roll through the bots, and somewhere in between there we'll form secret alliances with each other and go to war on the others with armies of suicide bombers or Ivans or what have you (crono ivans and crono commandos are particularly effective), and the game will end hours later with two of us still standing and about to go to war on each other when the game freezes due to having too many units/explosions going off at the same time.