Quite a nice game. But on the long run tends to be quite repetitive. Good thing that there are the sub-missions.
Good thing which keeps you going are the mini-missions which will be found during respective levels of the game.
Not such an easy game, quite long and hard to go through.
Another thing which keeps the game quite intricate is the introduction of heroes within the game which give quite a certain edge to the game. Each hero comes with a unique set of special skills.
Expect attacks from the enemy at any time, so prepare your defences as quickly as possible. On the whole I can say that it is a good game!