I'm home today with a sprained ankle, which gave me the chance to read Dreams of Ruin.
Dreams of Ruin is a strong idea that's clearly been thought through. It describes how a negative energy ecology suitable as a campaign-level threat to challenge high level PCs works, and provides a model for the various subcomponents involved in running it - sample encounters, information on how to run and adjudicate the PCs setting up a research laboratory or magically rewriting society and landscape to fight it, the colossal efforts necessary to cure / banish / control / weaponise it, etc. The ideas are well-done, interesting, coherent and nearly exhaustive. Even if you didn't want to use the Forest of Woe exactly, you could adapt a lot of this material to any sort of depersonalised creeping interplanar threat. For example, if you run Kevin Crawford's Red Tide setting, you could pull out tons of material here and use it with minimal conversion to depict how the PCs drive back the Red Tide itself (it helps that both settings are Labyrinth Lord ones). Or if you have a chaotic blight that threatens the campaign area a la Beyond the Wall: Further Afield's new threat pack, you could do some easy price conversions (I'd divide all prices by at least a thousand gold) and use it to run the blight in conjunction with the threat pack. The research component is especially well done, including handouts that chart out research paths for potential facts you can discover (while under tremendous time pressure that the book lays out clearly and in great detail).
The main flaw of the book is basically the same thing as its strength: Its singularity of vision. Dreams of Ruin sets up the Forest of Woe as something that stories and adventures spin out of, but it only gives you some rough guidelines and ideas about what those stories and adventures would be. In particular, the book could use a table or set of tables that cover "What is the weird magical material your research project requires?" "Where is it found" "Who controls it?" Magical items required for things like research are laid out (including building a device that requires 60 Gems of Seeing) but a lot of the other devices / spells / options just basically say some variation on "Spend an ungodly amount of money". Having a larger master table of random magical junk could either replace the pedestrian gold costs, or augment them with concrete detail ("So, uh, I rolled that you need 100,000 gp worth of Titan spittle," or "You need the baculum of a leviathan, and six rare flowers of eternity to build your Automatic Augerer"). (Edit: You could repurpose the system it gives for breakthrough critical items that refers you to the LL AEC, but that still wouldn't help you come up with who owns it and where they are, and what you need to do to get it).
It might also be useful to have a random high-powered NPC You Need to Recruit To Your Research Team table that covers what they want ("We need to recruit the Witch-Queen of Blagoblag - she wants the Gem of Guzzendle as payment") to spur ideas.
Similarly, the prolixity of the book is greatly appreciated in some areas (describing how the Forest of Woe works; facts PCs can find out through research; elaborating on the challenges of liquefying a god and running them through an oil pipeline) but less so in others. In particular, the sample encounters are overwritten, and could be more concise. It took a second read and the memory of a picture a few hundred pages back to realise there were devil mechs in one encounter.
Overall, I think it's a good book to pick up (especially because it's free) if you're trying to get ideas about how to run high level campaigns. There's a lot of material and structures here that, even if you don't adopt them directly, should serve as a useful model for how to structure such material in your own game.