I didn't find it particularly funny (and I love spaced) but the GF absolutely loved it. I thought it was brilliant in places, but too long overall. I was somewhere inbetween a massive head-ache and falling asleep by the last 20 minutes.
And the plot? Good lord, some people here are complimenting it! It was quite poor. It doesn't matter in a film like this of course, but it would have been nice for it to have taken the mickey out of it's story arc a bit more. It really was Channel 5 B-movie stuff. That's fine, but it was presented (underneath the superficial jokes) as an overly serious narrative. Shuan Of the Dead managed the unfolding of it's plot better.
Fun film though, definately worth a rent. I love Simon Peg