Frontier Elite 2 - Has to go down as one of the most amazing and immersive games ever created. I remember reading the box and seeing that it could generate 100,000,000+ planets. There of course were some bugs but the complexity and scope of the game on one floppy disk was absolutely mind blowing. I spent countless hours perfecting my landings on planets, finding trade routes and exploring the galaxy.....i would even use the map to discover interesting planatary systems and attempt to fly there.
Sensible World Of Soccer - While again this game had a few bugs (namely lack of player stats?) the sheer scope and the amount of teams was absolutely amazing. I have yet to see a football game that matches the sheer size of this game and i remember playing in the variety of leagues it had to offer.
Theme Park - As far as im aware at the time the game was unique. I remember reading previews for the game and waiting in anticipation of it's release, read more reviews and finally got my hand on a copy...was amazed by it and didnt put it down for ages. There was a sense once you did one level that you'd already gotten most if not all the rides etc but the replay value was still high.