My opinion: While the rears speakers are used relatively subtly, there's excellent separation between the three front speakers, and that alone makes this 5.1 mix worth hearing, IMO. Also, the overall sound quality is excellent.
More importantly. I hadn't really listened to this album since I was a teen. Admittedly the first time I heard the 5.1 mix I was a bit disappointed with how relatively sparsely the rears are used, though I understand there are reasons for that. But the second time I got all the feels from my teenage years back (in a good way). IMO, the mix supports the emotionality of the album (in particular the vocals).
A few other things: the bonus features are fantastic. Best ones: we get the whole "Recital of the script" video, including "Grendel" and "The web," and we get a 1.5 hour documentary on the making of the album. (Side note on this: closed captions are available for this documentary. THANK YOU FOR THIS TO WHOEVER DID THIS.)
So, 9.