Repetitive, but great fun when played in small doses.
Hated the fact that it's so linear, the enemies are thick as, and at the end of the first play-through – you're told you've missed some stuff and basically have to do the entire game again (yawn), with a couple of extra areas (which look and feel the same anyway), hence I gave up half way through this.
If they made a sequel I'd want to see abilities to chain defences so you don't have to stop game-play every minute and press countless buttons, and perhaps having to enlist some help to defeat tough bosses would be a good idea.
I've still got the game saves, so if I'm stuck between games I might return to this, if someone says there's a real payoff for playing it to the end - Otherwise I'll keep it on the shelf.