Got this last night and played it for 20 minutes before bed once it hit midnight - managed to get 2nd on the 1B leaderboard thanks to playing it straight after release
On the bus this morning I played a couple more levels, the bosses in world 3 seem to be a good step up!
Are the powerups completely random? Runs at levels seem to go very differently depending on what powerups I manage to grab - especially if you luck out on the twin lasers. It seems to take a good 20 seconds to kill a turret with ordinary fire (and constant dodging), but get a laser and they're done in 1 or 2. I can see that making a big difference to high-scores.
I'm also not sure exactly how the overall score works - do you have to play through the game arcade style without stopping to keep it totaling up? I kept quitting back to the menu so I could look at the medals and leaderboards, which kept giving me a final score.