Ooooh...
There are so many games that are good so its really hard, atleast for me, to rank them. Its a bit like saying, whos the better musician without specifying which genre you're talking about
But anywho, here is my list of top 5 games in no specific order:
Civilization 1 & 2 (I really hate 3 & 4)
Any Sierra adventure game (I pretty much love them all the same so its really hard to pick out a specific game)
Tie Fighter (X-wing was good, but Tie Fighter took the game to a whole new level and you got to play as bad guy
Half-Life 2, HL2 Episode 1, HL2 Episode 2
Might and Magic 3 (This was the first M&M game I ever played and even tho I liked 4 & 5 they never came near 3 imo)
There are alot more games I could list, but with only mentioning 5 these are the ones that stands out the most.