Duke3D did have mouselook, yet it wasn't the default. The earliest mainstream FPS I can recall defaulting to mouselook was Future Shock (1995). Funny enough Quake also buried mouselook behind a binding/command you had to assign yourself.

Regardless, I agree SS1 was a classic. Yet even with the fan patches and modern controls it did so many things and was so hard I bounced off. Wish I had tried some of the skill adjustments but my pride got in the way. The reboot looks like a good chance to retry. After Deus Ex this genre has become my favorite.