Yeah Waverace 64 was frickin' amazing. The topology of the waves and how you had to anticipate and stratgise the interaction to gain the most speed was great. Also it had the extreme variance as the weather worsened, changing the approach to a course. Just a brilliantly delivered concept.
Waverace on the GC by comparison however was crap. Yes, it had a more 'wet' kind of feel, lots of effects and so on, but it lost that interactive feel with the water. It was more like a broadly undulating surface plane to be driven over, rather than something to be navigated moment to moment, getting bounced around.