it coulda used some sorta survivor mode after completing it. because you dont really have a chance to become the ultimate you can.
although.... i had 2 fully upgraded rockets, and 2 which had only been upgraded once. aswell as main maxed obviously. but it was just... slaughter..
also.. last boss. i found it easier than the boss on wave 20 by miles. last boss i didnt need to do anything and i won. that boss.... i only rly had a chance to kill once he stopped firing.
besides that it was an awesome and very addictive game. i didnt stop, for anything untill id completed it