The omnibus edition pictured here is the one I got, from my public library, and it contains all four of the Dying Earth "novels." I say "novels" in quotes like that, because two of them are clearly not novels, but rather "fixups"---a term for a series of short stories strung together into novel-length and with a few bridging sections put in to make it have a superficial resemblance to a novel. The first and fourth "novels" (The Dying Earth and Rhialto the Magnificent) are fixups, while the two middle sections, The Eyes of the Overworld and Cugel's Saga are proper novels, and in fact, a matched pair with Cugel's Saga being a clear sequel to Eyes.
I checked the book out, and also ended up renewing it the maximum amount of times that I could (three) for a total period of nine weeks. This, as you might guess, is already not a good sign; books that I really enjoy I can read in a remarkably short time, even when I'm busy, and clearly that was not happening here. In fact, I didn't finish the omnibus at all; about halfway through Cugel's Saga, the third of four novels, I quit and turned it back in. It wasn't strictly going to be due for another week and a half or so, but since I had been unable to muster the desire to even pick the book up since before renewing it---for a good two weeks---I finally decided that it wasn't worth it to try and force myself to read something that I clearly didn't really want to read.
I'm not sure that I can pinpoint my disatisfaction with the books. The fixups were relatively easy to read, as each "chapter" (formerly an unconnected short story) required little commitment. The novels, in fact, felt much like a fixup in that regard as well, the chapters were relatively self-contained narrative modules, with only a loose connection between them. The "hero" of the two novels, Cugel the "Clever" was a reasonably entertainined protagonist; a con artist, basically, who thought himself very clever but who was clearly out-conned repeatedly.
Somehow, though, I found the whole less than the sum of its parts. While on paper, everything looked good with the books, in reality, I just found them difficult to read. Perhaps it was the lack of a compelling narrative focus. Because of the loose, almost short story like nature of even the novels, I found that the books were the opposite of a page-turner; when I finished a chapter, I felt like there was no compelling reason to immediately start reading the next one. The lack of any interesting or sympathetic supporting characters might be a part of it, the fact that Cugel, while charming enough at times is also frequently frustrating to read about, and the fact that each chapter being an unconnected vignette makes many individual chapters feel occasionally tired, pointless or skipworthy may be another. Coming as I am, from the standpoint of a fan of the pulp aesthetic, that may sound surprising, but the fact is, I can't read huge blocks of Howard, Lovecraft or Burroughs either. They're best handled if taken in moderation, I think, broken up with something else in between to remind you of what compelling novel writing is like. A diet of all short-stories over a prolonged period of time, is like a junk-food diet in a way. You can read plenty of words, but I---at least---find it unsatisfying over time. Maybe I should have approached Vance differently, and not tried to read all four of his Dying Earth books back to back as a huge chunk. In fact, I may yet come back to it to finish it later, but I can't do it now. I'm just a little burned out on the format for the time being.
All in all, I don't dislike Vance as much as I dislike Moorcock (another "classic" fantasy author, pivotal to D&D, who's writing actively turns me off) I just found it... unremarkable. Not my thing, I suppose. In fact, I figure that Gary Gygax and I might have been at loggerheads, if the occasion had ever come up, in terms of what fantasy is good. Not only do I not like Vance or Moorcock very much, but I'm also not a fan of L. Sprague de Camp or Poul Anderson (although I admit to not having read the particular books of theirs that were most inspirational to D&D itself)---whereas Gygax expressed a certain level of disinterest in Tolkien, who I consider to be completely brilliant. Maybe it's somewhat generational; Gary was more or less my parents' age (a few years older, but since my parents had me at a young age, he's almost exactly the same age as the parents of most kids my age) but I'm not so sure. I started reading fantasy fairly young; before it became a boom genre for the book publishing business, and as such, I was fairly steeped in the so-called classics from a youngish age.
In any case, now that I freed up my "fiction reading slot" I actually picked up some J. K. Rowling again. Watching the Harry Potter and the Half-Blood Prince movie reminded me that I didn't really recall the details of that book (or the next one) very well anymore, so I'm rereading them, probably back to back. For what it's worth, I've read more than half of the lengthy Half Blood Prince novel in just two days, so I'm flying through it, especially relative to my speed chugging through the Dying Earth novels. After I finish that, I plan to belatedly finally pick up the next Erikson book, Deadhouse Gates. The fact that I went from a dissatisfying novel considered a classic by many fantasy fans to a Harry Potter book may say something about my tastes to my loyal reader or two, but be that as it may, one thing I think it's difficult to refute about the Harry Potter books is how easy they are to read, and how they very successfully manage to suck you in with 1) likeable, readable characters, 2) reasonably entertaining plots and 3) an engaging setting. I'm not sure that Jack Vance managed even one of those points well.