Acantophis3rD: Even Doom didn't had the mouselook we now know, but it was possible to implement it, even back then. So why isn't it part of the SS experience? Deadlines?, lazy designers? or they simply never thought it could elevate their game?
Stop saying dumb things. SS1 does make full use of the mouse, just not in the same way that modern games do. In SS1, the mouse is used for aiming, activating buttons on the interface, and drag-dropping items into your inventory. How many FPS games had drag-and-drop back then? The SS1 interface is, in all regards, a technically advanced piece of work. But it came from an era when both mouse control and first-person gaming were new, created by designers fresh from Ultima Underworld, a complicated, slow-paced, simulationist RPG. As such, SS1 ended up with an interface that was far more expressive and granular than it needed to be, not well-suited to a fast action game.
Their next first-person project, Thief, can easily be seen as a direct response to SS1's overcomplicated interface. All the same posture controls that SS1 had are still there, but stripped to the bare essentials. A simple binary lean instead of SS1's analog lean. Simple crouching instead of SS1's dual crouch/prone system. An utterly minmal HUD, compared to SS1's baroque, animated, screen-framing HUD.