In reading reviews of my previous games, I've found recurring comments about artwork. Either there is 1) not enough, or 2) it's too cartoony.
That first one is easy enough to address. In fact, I have. Mythweaver: Legacy weighs in at over 80 pages, and it has an average of one illustration per page. A handful of pages have no illustrations (because they layout wouldn't allow it, and I didn't to bump the text on that page to a different page and break up an important concept over several pages if I didn't need to); several pages have 2 illustrations. My previous 'best' art to page ratio has been about one illustration every four pages, and I usually aim for about one illustration every 5-6 pages. I'm always striving to keep the page count down to keep printing economical and to keep information together. This one has more breathing room, although changes I made to the fonts and some layout choices have allowed me to pack a little more text in anyway.
The second one is not so easy to address, and also not something I particularly care to. My favorite classic D+D illustrator was Jeff Dee, and a close second was Jim Holloway. I LOVED Holloway's cover to Dungeonland. Jeff Dee is a comics guy. My inspirations are all 'cartoony' guys. It's what I love. I've tried to draw more gritty illustrations, and they always fall flat for me. It's just how I draw. I can either decide that what I do is good enough, or hire someone else to do the illustrations. In truth, I love some of my illustrations, like the vast majority of them, and feel 'meh' about a handful. Of course, I feel that way about the art I see in pretty much any game; I could invest a huge chunk of change and get results that are comparable to what I have now, at least from my point of view. And then, it wouldn't be me fully reflected in the text. So, I can say I love my art, and if people don't like it... well, they don't like it. Not much I can do.