Sol 3791, September 22, 2014. Ulysses Crater looks lopsided because it was formed by a meteorite impact on the sloping surface of Wdowiak Ridge. (Also, the meteorite likely struck at an angle to the surface itself.) The result is a crater which from ground level looks unlike the classic bowl shape many impacts display.
The sharp-edged blocks lying all around are probably pieces of ridge rock which were thrown into the air by the impact and fell close to the crater. Since the impact, winds have carried sand and dust up the ridge slope and dropped them into the crater.
Opportunity raw images, its latest mission status, and a location map.