I am a huge Wipeout fan. I have got all all 6 versions of it from the original to the latest PSP affair and I am eagerly awaiting the release of
Wipeout Pulse in spetember. 5 versions were (and still are) very playable and I go back and play them over and over even the older ones. The only version not worth the disc it is printed on is
Wipeout Fusion, the PS2 version. It was written by a different coding house to all the others and is very poor.
I think one of the best features of Wipeout is the high score system. I know that sounds pathetic but it is the reason I keep going back to it and why I keep going back to older versions. You can score a fastest race and a fastest lap on ever circuit in every speed class and it also tells you which ship you were using. You can see at a glance if you hold the records and if you have a gold medal, so there is a huge insentive to beat every circuit in every class.
What I always wanted from the PSX and PS2 version was the ability to merge your high score with a friends. You would put both memory cars in the machine and it would create a new high score table based on the scores on both cards. Now, with internet connection, an online system would be far better.
There was an online system created around the time of
Wipout3 but it was floored because the user simply entered his/her high score manually, which is of course very open to abuse.
So, in summary: The gameplay is very important (see Wipeout Fusion) but it is the insentive to progress that really keeps you going back to it.
I love Wipeout and if you can create something playable you will be my hero. If there is anything at all that I can help with, I would be very willing to assist. I would be most suited to HUDs and 2D work, just let me know
[Edit] Having just read VanB's post it got me thinking. I also love Trackmania and a combination of Wipeout with trackmania would be incredible. Think Grungy Wipeout with a track editor