* Age of Empires 2
* Alpha Centauri
* Baldur's Gate
* Counter-Strike (the original mod!)
* Freespace 2
* Heroes of Might and Magic 3
* Homeworld
* Jagged Alliance 2
* Outcast
* Planescape: Torment
* Roller Coaster Tycoon
* SimCity 3000
* System Shock 2
* SWAT 3
* The Longest Journey
* Unreal Tournament
I've (re-)played several of those (BG, HoMM3, JA2, RCT, Ps:T, SS2) in the past couple of years and at some point realized that they were all released in 1999.If you include the 1998 Christmas market, you can add at least:
* Falcon 4.0
* Fallout 2 (definitely should've been delayed until 1999!)
* Grim Fandango
* Half-Life
* Myth 2
* Thief: The Dark Project