About my 30-21:
30. Myst III: Exile (PC)
Best of the series in gameplay.
29. Halo: Combat Evolved (PC)
28. Indiana Jones and the Fate of Atlantis (PC)
Possibly best of the Lucas adventures in gameplay. I miss the time when "Indy 4" meant this.
27. Final Fantasy VI (SNES)
26. Full Throttle (PC)
Another beautiful Lucas adventure, with unique puzzles. Rather short and would be higher without that fighting bit.
25. Colin McRae Rally 2005 (PC)
While certain cars are horrible to drive, the game does so many things right.
24. Pokemon Crystal (GBC)
I've played four first generations and this was the peak.
23. Populous (SMS)
Master System pad is better controller for Populous than a mouse.
22. Dragon Strike (PC)
Dragon flight sim, use lance, sword, breath, claws... or land and let your dragon eat a few people!
21. Crush! Deluxe (PC)
Turn-based violent scifi sports strategy. More satisfying against two human players, the simple AI only wins by luck. But really wonderful game nevertheless.