First off, let me just say that I've only watched .Hack//Sign up to the end of Gestalt. Also, this is more of a review on the series up to this point, rather that Gestalt alone. You can form your own opinion from that.
Now, at first I loved .Hack//Sign. I was captivated by the entire concept of character relationships inside an online game. But soon, the effect wore off. The episodes became so bland and monotonous, even major events in the series (like the last episode in Gestalt) failed to rekindle my interest in Tsukasa's plight. Most of the scenes just feel like filler... as if .Hack//Sign, up to this point in the series at least, could have been done with half the episodes.
As for the soundtrack, it's mediocre. A few good instrumental songs, but nothing to scream about.
But if you like the .Hack video games, I'm sure you will enjoy this series more than I. It just seems to me that there are better animes out there that focus on character development... even if they do lack .Hack//Sign's original concept.
If you've sincerely enjoyed .Hack//Sign up to Gestalt, then you will most likely enjoy this DVD. If you're having doubts about where this series is going, than you may want to save your money.