I only have Vol. 1, but I thought that the translation was decent enough. The problem is that the fansubbs were meant for the more experienced anime fan (people familiar with honorifics and such), while the Geneon’s release was subbed more casually so that anyone could enjoy it.
However the release itself looks like a rush job, possibly even low-budget. There are very few extras, and the “extras” and “languages” sections were combined. The DVD lacks a lot of polish (especially comming from Geneon). Tsukihime has a huge cult following in the anime world and I was expected something more.