I'm tired of being all negative, let's change the attitude a little, make it a bit more.. well I won't say "friendly", but polite/constructive at least. Forget that petition, let's just show GW what we think could be done better.
I don't think you can necessarily split the artwork in the book into broad categories based on when it was drawn and make definitive statements about all drawings in that category. Let me give you an example, the picture I like least in the entire book is the cold one rider on p.19, this is, I believe a 6th edition piece (produced at the time of the Lustria supplement and used as the saurus cavalry box art, which was before 7th edition) as the style is very cartoony and the rider and beast both look very awkward. On the other hand the carnosaur art that was produced at the same time (the Lustria supp cover art) which is on p. 50 is one of my favourite pieces. I'm also not a huge fan of the Saurus artworks in the bestiary section on p. 32, 34 and 35 as there is a certain unnatural, awkwardness about them, two look like they are the process of tripping up (Saurus leader and cold one rider) and the third is hefting his halberd in possibly the most awkward way imaginable. These are all 7th edition pictures, I believe. I actually really like the softer, slightly pastely style of the troglodon art on p. 37 and the Ripperdactyl art on p.43but on the other hand there are 8th ed pieces I'm not very fond of, the skink leader on p.36, Kroq-gar on p. 51, Tehenhauin on p.56 and the Saurus BSB with the skaven pelt banner on p. 62. Overall I think my three favourite pieces in the entire book are the temple scene on p. 4-5 (which is 8th edition), the art on p 28-9 (which was the 6th editon cover art) and the Bastiladon art on p. 48, which again is 8th edition. Furthermore if you compare the artwork in the 8th edition book as a whole to the artwork in the 7th edition book it is far, far better overall. There were so many really awful pieces in the 7th ed book, such as the mis-proportioned, cartoony piece on p. 5, the 'nurgle-Slann' on p. 9, and the art on p. 11 (not even sure what that was supposed to be), the piece on p.28 of a creature which looks totally unlike any of the Lizardmen range at the time (sort of a Saurus with the head of a Stegadon), and the old Gorrok art on p. 67 is almost painful to look upon.
Possibly, but my feeling is that 7th edition was a real 'dark age' for Lizardmen artwork, which we are only just now coming out of. I don't think we are at the standard of 6th ed's best though, but most of the8th ed artwork is a far better standard than that produced in 7th edition. I'm not sure it matters particularly all the best 6th arts are in the 8Ebook anyway, and they do seem to have got rid of the awful 5th edition drawings which have blighted the last two books.
Most of the pieces you say you don't like seem to have very similar styles. Same artist? I like the vast majority of it to be honest. However, the new Slann art, the bastiladon art are a couple of faves, but the piece on page 4+5 really takes the cake in my opinion. Awesome.
There isn't a whole lot this approach achieves. It's more like wishing the problem away. I would suggest taking a more proactive approach and sending an email to customer service outlining dissatisfaction with WIP marks and other qualities which are unsatisfactory and at least then it can be said we let them *know* something was wrong in the first place. Don't rant, swear etc, just a reasonable letter stating the problem. The rest (artwork) is entirely subjective, so that's for the individual to decide. Personally I'm inclined to favour the older artwork, but that's because I'm not much a fan of the newer water-colour/smudging style.