Late call for this, but the youtube channel Lewis and Ben Save the World has both Terror from the Deep and modded X-Com on it. TFtD videos there should give a good idea as to how it runs. In regards to graphics, given they’re sprites and not 3d renders I consider them to hold up substantially better over the years (especially with the return of retro aesthetics,) compared to things released even five years ago.
Get XCOM enemy within and then play the mod/overhaul Long war. I played over 1000 hours thanks to this mod. Very, very hard and very deep.