I'm a huge BtVS fan and own the whole TV series on DVD. I've really like most of the Season 8 comics to date. Volume 4, if you are collecting the graphic novel format versus the individual issues, is the weakest of collection so far. While I did enjoy seeing the Fray characters again, it felt like more of a stunt that a real plot point. The Willow portion also felt unsatisfying as well, sorry its hard to explain while trying to be vague to avoid major spoilers.
The side plot of Dawn, was, in reality, kind of stupid. I appreciate that they wanted to add some more fantastical elements that cover ground they could do in a TV show with a moderate budget, but this was beyond the spirit of the series. The "there are consequences to relationships" is very Joss, but the results here feel like fodder for a few quips and jokes rather than a solid allegory.
So while I'll tune into for another volume, my passion for this version of BtVS is waning and will be gone without a solid set of issues and some new meaty hooks to build my desire and suspense for a volume 6.