In no particular order :
1. Gothic 1+2
2. TES III : Morrowind
3. Baldur's Gate 2 : ToB
4. Civilization IV
5. C&C : Generals
6. Half-Life Series
7. Planescape torment
8. X Com : Enemy Unknown.
9. Heroes of Might and Magic V ( yes V,not III. I feel it's an updated III with some of the good elements from IV).
10. Diablo II : LoD ( more like Eastern Sun but it#s not that relevant )
11. Warcraft III
12. Painkiller!
13. Jade Empire
14. Kotor (Both)
15. Castlevania ( Super Castlevania IV + symphony of the night)
16. Divinity Series
17. Souls Series
18. Total War ( Rome 1 and Medieval 2 )
19. Neverwinter Nights Series ( Hordes of the Underdark for 1 and Mask of the Betrayer for 2 )
20. Unreal Tournament 2004
21. Jedi Knight 2 : Outcast
22. Rise of Nations
23. Ultima Underworld
24. Prince of persia ( the sands of time trilogy )
Those are the games that really had an impact on me and I truly consider great. There are some more ofc but I'd have to make a top 50 at least to cover all the games i think are 10/10 material from me but these ones really stood out for me.