Didn't get the Ultima series so never experienced that one, but an Origin Systems game I loved was System Shock. Still unbeaten in my book for raw experience as an early FPS RPG... so damn scary. It had so much complexity to the plot, it really set the bar high. I don't think it was matched until 15-20 years later ... many far more popular games were pathetically linear, simplistic and mono-dimensional by comparison. Other early games which left a mark for me: Heretic (which for unknown reasons performed very smoothly on my graphics hardware - Oak?), Descent (first really 3D game, excellent gameplay and many overnight sessions with friends), Dune II (defined the RTS genre on PC), Mechwarrior 2 (strongly immersive and awesome experience with a proper joystick), X-Wing/Tie Fighter (strongly immersive). Later, Command and Conquer (first modern RTS), C&C2: A Bridge too Far (awesome top-down historic battles via modem). Ahh, these days why do all the games seem so rinse-and-repeat... I think the last one I played that really impressed was Shenzhen IO.

PS. Hey that's cool you're in Sydney. If you want a drink tomorrow night drop by https://www.meetup.com/turingcircle/events/299581949/ at least a couple of us are going.