Coming from someone who started Gantz last month, and stopped right before the final phase while waiting for the manga to be completed - I thought the final arc was probably a good arc too, although the 'final battle' was a little bit ridiculous. If anything, I'd say that the Nurarihyon/Osaka arc was somewhat boring compared to the other arcs simply because of the aliens that never seemed to die. The final arc has a different atmosphere - more shounen like opposed to the dark and depressing Gantz we had initially all the way up until the vampires. For those who're complaining, I'd suggest reading the whole final arc in one shot again. Sometimes, waiting for chapters to come out every other week just destroys the pace and mood (looking at you, Bleach.)