Not hard really
Games are alot harder to score well on. MAN I HAVE No Life so i play alot of games so i can be very critical.
This game was easyier than i thought My first go i got to lv 21 A- which i thought hey, that wasnt bad =]
Unfortunately i didnt want another go so it lacked playability.
What always grabs me is a 2p game. Have some sort of "Party Mode" in your second version to allow 2 people to play and have a load of mini games or styles of verses matches.
e.g.
1) High score. first player to destroy 100 missles for e.g. with a blue and red coloured cude each player controls one with WASD or UP,DOWN,LEFT,RIGHT.
2) Destroy each others Bases, turn based missle launch thing. I duno im just brainstorming.
Your game your rules.
Very good game on the whole x