Not in any particular order:
Thief 2: The Metal Age
Star Control 2
Baldurs Gate 2
Vampire The Masquerade: Bloodlines
This stuff changes all the time for me though,there´s always some that always stay on that "top 10" but others keep switching in and out depending on my current disposition,other ones like Kingpin: Life of Crime,Ultima VII,Skies of Arcadia,Hearts of Iron 2,Freelancer,X-Com UFO Defense,Grim Fandango,Starcraft,Rome: Total War,Riven,Quake,Blade Runner,Phantasy Star 4,SHOGO: Mobile Armor Division,Geoff Crammond´s GP3,among many others could´ve also made that list,wich is why I always find really hard to choose just 10 and when I do I rarely put them in order,if I had to choose the overall favourite it would most likely be Deus Ex but after that I can´t really put them in any order.
Star Control II is a great game, but the combat was a disappointment for me personally. It was the one aspect of the game that stopped it becoming 'awesome'. I wasn't that good at it, and maybe that dampened the experience, but I really couldn't get in to it. The rest of the game, exploring the galaxy, finding elements and supplies, trading and forming allegiances with alien races, was fantastic.