Personally, visual clutter and poor performance were two major factors why Wave didn't work for me. Visually they were cramming too much stuff on the page, with loads of avatars / icons for participants and the like - IMO unnecessary information to have on the landing page. And performance wise it was just not good enough, maybe if they made it an optimized native app instead of a webapp.

At least they could incorporate the tech they developed and used for Wave in other products, notably Docs and G+.