Well, the main appeals for me were:
1. Its fecking MAHOOOOSIVE inside. I'm a big lad, and if people sit behind me in most cars, they are struggling for leg room. I hired a Mercedes C class recently and you'd need to be Hornswoggle to sit behind me in it. In the Superb, there is so much rear leg room (more than a Mercedes S class) that I can sit behind myself. That comes in handy when you are driving family and friends around. The boot is also enormous - easily bigger than anything else in its class.
2. Its got rock solid German build quality with German engines, gearboxes, running gear, etc. Its all Audi/VW underneath, which are totally reliable and not expensive to replace if anything does go wrong simply because of the volume of them produced.
3. The performance is excellent. Its a big car and yet does 0-62 in 8.7 seconds and will sit at 140mph all day long. It also returns as much as 60mpg.
4. It rides really really well and handles very nicely
5. Its stupidly well equipped. Leather, dual zone air, electric heated memory seats, cruise control, front and rear sensors, park assist, adaptive bi-xenon headlights, electric windows and mirrors, voice activated sat nav, voice activated phone integration, full iPod compatibility, automatic tyre pressure sensing, tiptronic DG 6 speed gearbox, and that's just for starters.
6. Its £6-8k cheaper than the equivalent Mercedes or Audi
7. I happen to really like the look of it. It doesn't shout about being rapid and its not got that "I'm a cock in a Merc/Beemer/Audi" quality.