Actually I'm pretty sure that omni must be acceptable because, to be honest, the Jasper Fforde omni in The Big Over Easy could have been done better, yet his book was published. Fforde possibly suffered by being read right after Anthony Trollope's The Way We Live Now and Jonathan Strange and Mr Norrell, but there were several places where I wanted to start editing the POV changes. Despite this, I enjoyed the book because other than the POV Fforde did an awful lot of things right.
Someone wrote an excellent post recently about why books are published. (I can't now find it, so perhaps it wasn't on LJ but on rasfc.) But anyway, they said words to the effect that next time you're picking a book apart and thinking, "Why did this crap get published when my wonderful masterwork has been rejected N times?" just remember that the author must have done something right. The publisher is looking to sell books, not publish the Perfect Novel, so as long as the faults are not going to impair the enjoyment of the parts that work, readers are going to be forgiving and will overlook the faults in order to get their hit of whatever it is that turns them on.
Different readers, of course, will forgive different things, so if something really really grates, then the book is not for you. Simply put it back on the shelf and look for something else. There's plenty of choice. So basically Jasper Fforde is doing enough right (a complex and satisfying plot and his usual bizarre yet somehow believable characters) to carry the book along and it thus gets by with merely acceptable prose. To anyone who likes rich and stylish writing, however, his book would be a disappointment.
Finally, while I'm in random thought mode, the reason Jasper Fforde's book is not quite up to the level of his first three (IMHO) is that it was actually written before them. At least I believe that is the case, from reading his web page. It was the one he'd failed to sell before finally making the breakthrough with the Thursday Next novels. But it does lead to musings on whether it's better to let unsold early novels stay languishing in the drawer and move on to new things rather than let later success lead to the publication of earlier, less polished stories.
It will be interesting to see what happens in Fforde's future novels. There is another Jack Spratt and Mary Mary police procedural in the pipeline. And yes, I'll definitely buy it because The Big Over Easy did exactly what I wanted: provided an amusing diversion for a few hours. As long as he keeps amusing me, I'll keep buying.