From a technical point, my favourite is F1GP. There's just so much "new patch tech" in there it's hard for me not to have a soft spot for it. Without F1 there would be no ULSv3.. and without ULSv3 there would be no F1, as it was developed alongside the patch.

WoD is also a very nice one, although technically not as demanding as F1GP was to fix (even with the Amiga music) it was still a thrill the first time the TFMX played without crashing.

*HELD BACK* is also one of my personal favourites, nowhere near as complicated as F1GP, but it still required a ULS_EXECUTE command, which I always find fun. (Will be released 'yeah, around then I guess')

As for gameplay, I always had a soft spot for Midnight Resistance.

I can't stand Xenon II - it's too slow, and the music is dreadful. In fact I don't really rate the Bitmap Bros games much at all - they remind me of psygnosis - all glitz and no depth.