Well I had a chance to look the Manual of the Planes over this weekend and read some of it. My initial reaction is perhaps a 5/10. It just didn’t strike me as much as say the Draconomicon did. It read very dry and left me very much Meh.
But in its defense in 20 years of DM’ing I’ve never gone astral traveling although I’ve certainly gone plane jumping but more of a Slider’s kind of thing to use perhaps a more widely known reference.
It both feels short and reads short, without having it here at work, I’d guess maybe 150 pages? Most of the sections are short and while perhaps evocative, not filled with a ton of information. I’m certainly not a “need the full recipe with step by step to enjoy my banana bread” type of GM I do want a little more than “use flour, sugar, eggs, bananas to make yourself a tasty treat”.
YMMV as always and it’s certainly better than nothing but…
You’ll get a few pages for the planes as they exist now, Feywild, Shadowfell, Astral Sea, and the Elemental plane and that’s pretty much it. Each of those is broken dow into anywhere from 1/4 to 1/2 a page of information describing some of the points of interest in each plane.
Another chapter will give you a few (very few) new critters for the PC’s to run into and are most devils/deamons that IMO should have been in the Monster Manual but that’s a bitch of a another color.
It’s rounded out with a few pages on new paragon paths as related to planar activities, some new rituals, again dealing with planar travel and tracking and the like and a few new magic items.
All in all none of it is really jam packed with goodness to me. Â Sigil gets about 4-6 pages and is about the most indepth individual location as described.
So if you want planar travel and you want to make sure it’s based on official stuff so you don’t end up going old school and your players are all “uh that’s not right” then get it. But unless you have pressing need for planar travel then it’s value is iffy.