What about their Christmas-New Year art contest? It was a bit more than one month long, and there were only 33 art works declared. Some users even managed to present several art works. 10 winners. The chances to take last place and get 300 bucks was around 33.3%. By looking at the works, if a participant put just a little effort and don't participate just to participate, his chances to win were rather high.
Roobet art contests are easily some of the best contests in this forum. I won one of the prizes in their recent art contest and I agree with you regarding higher chances of winning thanks to around 10 great prizes.
The Roobet was a great help to a lot of members of the forum that have drawing skills. The contest started just like yesterday and I didn't believe it will last long like this to the extent that other gambling sites also see the art contest as a medium of advertisement to attract new users.
I respect the people within the Roobet that introduced the contest.