In a good level Graphics mean a lot, but NOT everything. The level needs to be exiting, but not too hard. It needs to be clear, so you don't get stuck in the half of the level. And most important of all, you need to have fun in it.
It also needs to be quite big, so you don't beat the level in let's say 1 minute, and there has to be a lot of change in the level.

According to these demands I'm going to judge a few levels from games:

G = Graphics
E = Exitement
F = Fun
B = Big
C = Change

1 = worst, 100 = best

Level 1
Game - Banjo Tooie Level - Hailfire Peaks
G: 100
E: 95
F: 97
B: 100
C: 100

Average: 98,4

Level 2
Game - Jazz 2 Level: Knight Cap
G: 65
E: 80
F: 95
B: 75
C: 90

Average: 81

Level 3
Game - Banjo Tooie Level: Jolly Rogers Lagoon
G: 100
E: 100
F: 100
B: 100
C: 100

Average: 100

(THIS IS MY ALL TIME FAV LEVEL!