I guess the title sums it up really, I was disappointed.

I'll try to not spoil anything (and I hope that anyone who replies doesn't either), but...

Plot - Basically ok, but not nearly developed enough. There's some bizarre romance thing that comes from absolutely nowhere without any build up. And Kris Kristopherson (sp?) was wasted.
Dialogue - Missing the humor and depth of 'Blade'.
Cinematography - Overuse of CGI. Unlike 'Blade' which made good use of CGI special effects, 'Blade II' seems to be an excuse for them to happen. I actually cringed a few times.
There was way too much attention paid to the vampires eating in gory detail that was just un-necessary and un-convincing. The fight scenes are messy and generally filmed too close, so that instead of the "Wow - cool move" effect, the viewer is often just trying to work out what he's seen. The locations were lacking in both depth and breadth compared to the first movie.
Sound/Music - Nothing special.

To sum up - Yep. It's a sequel.