The use of a thumbnail will really invite others to come play your game and you can see an increase up to 75% if you do this alone (from personal experience)
Now to the gameplay, excellent, once i got the timing down of the jump shots it became quit fun an engaging. Art was a little lack luster but considering how many graphics were used I thought it was pretty good level design with that in mind! :) Keep going I really enjoyed playing your game :)