First of all, all of the above and for the same reasons.
* Unreal - it was the first FPS I played and because of this it will always have a special place in my heart. This was back in 1999 and after having played many better FPS games after that I last year tried out Unreal once more. The feeling was still there: You wake up in a prison vessel on an alien planet and soon find yourself scared shitless just because of the sounds that meet your ears. You manage to find your way out of the vessel and you take your first look at the planet you will see much of in the coming days. You are amazed by the detail of this world and the waterfalls, oh the waterfalls.
By today’s standards this isn't a great game, but back then it was and I because I never had seen anything similar before, it had an enormous impact on me.
* The Longest Journey - the first shift was just amazing, and when the church doors opened and revealed Arcadia in all its beauty I was stunned. That was a great moment in my gaming life. The ending was also a once in a life time experience and when the game opened the sketches to me I almost shed a tear. That was one of the most emotional moments for me in any game ever.
* Outcast - You'll have to play it to understand. The screenshots don't show the whole picture. Although Outcast used old technologies, and the graphics was somewhat dated because of this, all the worlds in Outcast were and are extraordinary beautiful. You try to to find the highest place in every world and just let your eyes absorb the candy that is Outcast.
The AI of the characters is also something that amazed me. They all have their own things to do and they'll do them if you don't disturb them. They also react to shooting very well. The friendly guys tend to duck to not get in the line of fire. The hostile guys, well, they tend to shoot back.
Also, if you've shot someone friendly and another friendly guy sees it, he'll refuse to talk to you for some time, which was a neat trick IMO.
