Even after you get a million, there is so much to refine.
Actually, you can get a million and still be an extremely mediocre player, which is where I would rank myself.
With the super spray, you basically get a free pass through one and a half boards per loop (after the 24th board, and 2+ boards up until then), which makes up an enormous chunk of the million. So you only really have to survive and bughunt through one and a half boards per loop, and even then there are enough points available to die up to twice for the game to hand you enough extra guys to still tread water.
Without the super spray, I rarely can get through a single blue or grey board without dying at least once. Shit just gets too crazy with all the worms and Kong slipping off the rope, no matter how hard you try to keep all those plates spinning. I can only pass the boards because everything resets after I die and the crowd is thinned out.
Also, the queen bees are just hell. UGGGHH. If I have one complaint about the design of this game it's that the hardest, most teeth-gnashingly agonizing problem you face is not the effects of an enemy attacking, but it dying.
Though the bullets are certainly capable of delightful little surprises too. It was extremely evil of them to make it so that the bullets are still "live" after you clear the board. Bullet-related shenanigans have caused some property damage here.