This is only a review of the first part of the book: Dead Titans, Waken! I have not read Invisible Sun.
Dead Titans is an early draft of a novel that was eventually revised and published in 1948 by Arkham House under the title, The Web of Easter Island. This Centipede Press edition, published in 2011, prints Wandrei's original manuscript for the first time. I'm not entirely familiar with the differences between Dead Titans and Web, but I have confirmed that Wandrei extensively revised the ending before The Web of Easter Island was published.
I found the early portions of the story to be very effective. Lovecraft's Call of Cthulhu seems to have been Wandrei's primary inspiration. The pace begins to flag as the main character travels to Easter Island to stop an invasion of Earth by the so-called "Dead Titans," who are far from dead and instead inhabit the fourth dimension. Consequently, they can touch down on Earth at any time, whether it be now or many centuries hence.
Wandrei seems hell-bent on outdoing Lovecraft with florid descriptions of cataclysmic, cosmic events. These descriptions go on for pages and pages and instead of building horror or suspense, they just bog the story down. Wandrei's stylistic gifts are nevertheless impressive, so I'm willing to look past some of the resulting structural damage.
The ending of the novel contained some interesting material. It is set in the far future of Earth, and Wandrei seems to have anticipated something similar to the internet.
I'm now looking forward to reading more work by Donald Wandrei. Years ago, I read some stories from Colossus, a science fiction collection published by Fedogan & Bremer. At the time, they struck me as somewhat clunky and juvenile, so I didn't read many of them. F&B did a follow-up collection of fantasy and horror works by Wandrei, so I just ordered a copy and hope to dig in soon!
A final note: while this Centipede Press edition has beautiful artwork and is handsomely bound, typographical errors plague page after page. Some of the errors were bad enough that I had to stop and puzzle out the intended words. I think I succeeded for the most part, but it was very distracting. I believe that F&B eventually published a paperback edition of this book. I'd be curious to know if they corrected Centipede's (or should I say, S.T. Joshi's?) many errors.