The first "phase" of Gantz ended around 240 chapters into it. While I have since read up to chapter 272 (the latest chapter) there are some thoughts that I had while reading.
1. In the last entry I said something to the effect that I wanted several of the characters back. Looks like that's not as far-fetched as I thought. This series is approaching DBZ levels of resurrection.
2. The fights still drag terribly. Seriously, they get really frickin boring. The first few were great. The very first in particular was excellent. It had only two aliens, one of which went down without a great fight. But it was tense, and visceral, and didn't outstay it's welcome. It was used to extend character motivation and was chilling in places. The current fight started about 30 chapters ago, and is still going strong.
3. There are still no significant advances in the plot. All we know is that there are some other Gantz spheres, and there may be a master sphere in Germany. The vampires are probably aligned with the aliens, but that doesn't stop them slaughtering each other if necessary. I really want to know more, but it doesn't look like I will any time soon.
4. The death of Izumi seemed a little quick. He had been built up for 70 or so chapters as a cool anti-hero. While his death is suitably epic, it seems like wasted potential.
5. I'll restate my opinion on the vampires. Seriously, katana wielding vampires are really original. Unless you count Anita Blake, or Underworld, or World of Darkness, or Buffy the Vampire Slayer, or any vampire fiction written since 1990. Why can't vampires go back to being solitary predators of the night? You know, scary.
6. Seriously. MORE PLOT! I read stories for the story. The violence is cool and all, but I really want the plot to kick in, and there's no signs of that happening soon.
Gantz has so much potential, but it seems wasted somehow.