I have a Cowon A2.
I bought a 770 to replace this when it was broken, and it just couldn't compare - much nicer to watch video on a Cowon or Archos.
However, video is VERY watchable on a 770 or N8x0 IMHO. With Nokia, watching movies is fine, the screen is big. I laugh at people watching viedo on a tiny ipod now.

So it does work well for watching video, but if thats a main function, a PMP like archos does it a lot better. One great feature of a PMP is you can zoom in and increase the picture that way (when cropping a little doesn't matter).
[I know you can do zoom on N8x0 too, but not easily).