One of all my favourite ST games was Where Time Stood Still
, a 3D Isometric adventure game from Denton Designs. It was only available for the Spectrum 128 and ST. While the Spectrum version was excellent it was a bit jerky and in B&W, the best version was on the ST since it was smooth and use grayscale for the windowed action area, making it really atomospheric because of the era it was set in. Some may remember The Great Escape on the spectrum, well this was a very much the same but a lot bigger.
I actually liked this game so much I did a map of it, it was a true epic undertaking beleive me. The instructions and tips can also be found on Guardians.