Sadly, art like that deters me from buying the products, and they may actually be okay otherwise.
As to the Kieth works, I've got a number of them including my latest, the Seven Pillars of Urquayd'n, and I think the *adventures* are excellent. They've generated some excellent traveller materials. Most of the interior art was... okay. Since I don't buy a RULEbook for the *art* (but for the RULES) and I don't buy an ADVENTURE for the *art* (but for the ADVENTURE), I accept 'just okay'.
I admit if the art is absolutely dismal, you wonder outright if the product is too. Passable art lets you at least focus on the content. Great content with great art is nice, but if I can only have great content and mediocre art or mediocre content and great art, I'll opt for the former every time.
For instance, for me, T4 was a product that (mechanics wise) probably wasn't too bad (ignore errata as I do when I think of MT which is my favourite iteration to date), but the art turned me right off. It isn't a question of gloss or colour or anything like that - plenty of CT suppliments were fine with minimalist line art, as were many JTAS issues. It is a question of being overbearing with imagery or distracting or of being so outright homely that one can't fail to be drawn to it (and cringe).
So, let's hear it for 'adequate' art!