Best Art: Luminous Angel
There are a couple reasons I really like the art for this card. First and foremost is just the quality of the art itself. The wings and the way the light plays off the angel's hair (especially noticeable in the foil version) just work in all the right ways. The other, more minor reason is the comparison to the old version. Now, Matthew D. Wilson's art isn't bad, but compare that art to this art and you'll see a clear winner.
Worst Art: Nimbus Maze
A friend of mine put it best: this is a watercolour background to a painting that someone spilled a little too much water on. It looks like there used to be art in the middle, but someone in editing decided to take it out (maybe it was too beautiful to behold with mere human eyes). I understand what Jason was going for, but the angle on the maze is too low and it just looks weird (look at Mystifying Maze for an example of what I think is a better angle).
Strangest Art: Massacre Wurm
I think this the strangest piece of Jason Chan's work simply because the wurm looks... way too happy. To me, it looks like it should be screaming "HI GUYS! I WANNA JOIN YOUR PARTY!!!". The art makes Massacre Wurm seem like the kid who shows up to your 11th birthday party, starts running around the house hyped up on sugar, and smashes face first into your mom's china cabinet, making it fall on the table with all your presents and your cake, ruining everything in the process.
I love Jason Chan's artwork. Even his worst artwork is really, really good. I just hope Wizards starts putting him to work on more common and inexpensive cards soon so I can have more artwork without losing a limb in the process.