Ignoring multiplayer games, I'd say the following were pretty weighty:
 
-Chaser (has something approaching 40 levels)
-Unreal (30+ levels, some of which were much bigger in scale than other games of that era)
-GTA:SA. Knew it would take a while based on the earlier games, but there's a lot of 'extras' in there too to suck up time
-Dawn of War: Dark Crusade. Some of the battles can last for hours; it's not quite as refined as Soulstorm.
-Doom3. For a groundbreaking FPS, this is fairly heavyweight at around 18hrs iirc. I think once I got to hell I assumed it was going to end soon.
 
There are other long games around like KOTOR, Deus Ex and Far Cry, but I pretty much expected that from them.
	
		
			
		
		
	
				
			-Chaser (has something approaching 40 levels)
-Unreal (30+ levels, some of which were much bigger in scale than other games of that era)
-GTA:SA. Knew it would take a while based on the earlier games, but there's a lot of 'extras' in there too to suck up time
-Dawn of War: Dark Crusade. Some of the battles can last for hours; it's not quite as refined as Soulstorm.
-Doom3. For a groundbreaking FPS, this is fairly heavyweight at around 18hrs iirc. I think once I got to hell I assumed it was going to end soon.
There are other long games around like KOTOR, Deus Ex and Far Cry, but I pretty much expected that from them.
	
 

 don't wanna complete it 
 then you realise there are other acts and wow 