I liked TFTD in general, it had what X-COM1 had with new aliens, new music, new tilesets, and a whole new game to explore basically. In a lot of ways it was like reliving the first game again but with an easier time learning it.
Unfortunately TFTD had a much more serious case of broken parts.
-broken research tree that it was nearly impossible to get through without cheating or knowing all the ins and outs.
-giant multi-stage maps with very serious 'last alien' issues.
-Broken difficulty (beginner was high difficulty, superhuman actually was impossible because you wouldn't detect any UFOs.)
-Generally more infuriating bugs, although the original had quite a few of those too.
One particular issue I had with TFTD however were the absurd technologies from a lore perspective. Psionics made sense to me on some level but Molecular Control? That's Absurd! Sonic Guns? Ultrasonic Grenades? Thermal Blades that work under water? Gauss weapons that work under water? Alien alloys don't work under water but plastic does?
I really got into Interceptor, it was very silly and campy. Clearly I'm not a good example of an X-COM fan.
I would have liked interceptor and I liked as much of it as I could get to. It was an example of perfectly decent X-COM and terrible flight-sim, especially if you tried to fly with a mouse.