These are in no order and are from multiplatforms:
 
1. SuperFrog (Amiga 2100) - Soft spot for this 2D platfromer 
 
2. Goldbox series (AD&D - Amgia/PC) 
 
3. Dungeon Master (Amiga)
 
4. Unreal Tourney 2004 (PC) - This game Lived on my PCs Hard drive for years!
 
5. Magic the gathering (Micropose version) - I still play the duel side of this game now and then eventhough the AI cheats!
 
6. ADOM/MORIA/nethack (multi) - Yes I'm a sad Roguelike game lover :P
 
7. Portal /Portal 2 - How could you not love this puzzler?
 
8. Half Life series  (Half life / Blue Shift/ and other variants/ Orange Box PC) - Best series Ever
 
9 Oblivion (PC) - one day I'll beat it , one day
 
10. Dungeon Keeper (Bullforg - PC) - Loved this game in it's day :)
 
....Given the list of games I own this is in no way my ALL time complete list - These are the ones I remember fondly :P