I figured this could be kind of interesting.... Title says the point of the thread really.

Fire Emblem... By a huge amount.

Let's see.

Fire Emblem: Radiant Dawn: 150 hours (3 playthroughs, Easy, Normal then Hard)

Fire Emblem: Path of Radiance: 40 hours (1 playthrough)

Fire Emblem: The Sacred Stones: 30 hours (1 playthrough)

Fire Emblem 7: 70 hours (2 playthroughs. Normal and hard)

Fire Emblem 6: 30 hours (1 playthrough)

Fire Emblem 5: 20 hours (I guess... 1 playthrough)

Fire Emblem 4: 30 hours (or something... 1 playthrough).

Fire Emblem: Shadow Dragon: 20 hours (some of that is in 09 though).

So... 370 hours, eh? That's without restarts though, so 400-450 hours.

Second is Team Fortress with 250 hours.

Definitely Guitar Hero, for me. I easily spent over 100 hours on Guitar Hero 3 (18 in one day), and most likely 200. I also spent a good 10-20 on Guitar Hero: On Tour and gave Guitar Hero World Tour 10 hours+ in the first four days I owned it.

Here's my top 4 for in order:

Warcraft
Ureal Tournament
Super Smash Bros.
Mario Kart

Advance Wars I guess.

World of Warcraft (don't really play anymore, woot)
Atlantica online
Final Fantasy X, XII
Breath of Fire 1 and 2
Metal Gear Solid 2,3,4

Fire Emblem!

Path of Radiance: 1 Playthrough
Radiant Dawn: 2 Playthroughs
Shadow Dragon 2 Playthroughs and halfway the 3rd

Fifa 09
Call of Duty 4 and World at War.
Professor Layton!

Advance Wars and Halo 3 probably.

i say

smash bros(280 hours!)

then mario (i played a lot on the mario vc games, like smb3,smw,sm64, and ofcourse some mario galaxy

then tied between guitar hero and mario kart(probably 100 hours each.)