Very addictive.
I think I prefer the leveling system in the first game better, but this was still a very fun game none the less.
I beat the last boss with elves before I unlocked the Angels. It isn't impossible, you just need good timing with sending out your titan unit so it has full hp and is on the opponent's side of the field when you destroy the castle. Make sure that the boss doesn't move from that area by sending more red dragons and titan units and you will be fine. For me, the boss didn't even get in the range of my arrows.