Whoaa… this is one of the anime that are worth looking for~~! And if you like even more gory details, wait till you feast your eyes on their manga, which I consider one of the most graphical manga ever!!!
By the way, is it me or do Gantz really end at episode 11? I say this cause I noticed the word FINAL at the end of episode 11, which I am currently downloading… Really hope it doesn’t end that fast, cause it’s really good!
Well, just me 2 sens 
might just be the final version of that ep, perhaps the fansubbers did a previous one too…