One game comes to mind. Hands down. I bought it because of the art. It was fantastic. However, the game system was … at best.. clunky. The game was Alpha Omega, published in 2008 (why does that seem so long ago now). A post-apocalyptic setting with angels and demons (like the series Dominion). It had amazing art and I used it for other games. I sold the hard copy of the game I had but kept a PDF of it for use in other games.
Artists included Matt Bradbury, Aaron Panagos, and Jonathan Standing. It was nominated for two 2008 ENnies for best production value and best artwork
I have a thing for monsters and creatures and this game had a ton of original creatures I wanted to bring into any of my games. Yes, at first I just wanted to run the game. I even sat in on a demo of it the one time I went to GenCon. But the system was just so crunchy that I did not see myself running it.
Then they released The Encountered Vol. 1 also illustrated by the same guys along with Erich Schreiner, Joe Slucher, Adam Bray, and Wes Louie. This was an incredible book with more and more monsters. Some of the best art in an RPG I have seen in a long time.
Sadly now the company is defunct, probably because the system was a hard sell.