Poor, poor Maura. He just wasn't the artist to choose for these cards (due to his style), but he get so maligned for it, so much more than he deserves...
Yeah, his work is generally pretty good. It just contrasts so sharply against the styles of the other artists, and that makes him stand out in a not-so-positive way. Although, while I can appreciate Shanty Town and Navigator on their own, I still just don't like the Harem artwork. I guess artists need to have something that are not that great.
I'm not all that familiar with game production, but I suspect that the reason there's not a consistent art style from a single artist is that it takes a long time to come up with these illustrations. If an expansion had to rely on one artist getting everything done, then it would never release on time (or be later than usual, if you're the jaded sort). I imagine that having many artists allow the production team to cleave more closely to the deadline.
I remember noticing this in On the Edge. Greg Houston's style was so different compared to the other artists, but it worked for the Satanist cards (if you're curious,
http://cdn101.iofferphoto.com/img/item/624/924/21/o_kL4JNQaDq4WPb0A.jpg)
But then, OnTE had a pretty diverse pool of artists, so it's hard to say that the game had a consistent look to it. At least with Dominion, the non-Maura cards look similar enough to have a general look.