Okay, so last year's games were solid but this is the real deal. This game is fantastic.
I was a big fan of the creative liberties taken as far as tower defenses go. Only a couple places to put towers, only three types of towers, and one of them requires the player to micromanage where its troops move. These creative choices are weird and unusual but ultimately make the game a lot more interesting.
I found pairing the cannon with tankmen worked well at the beginning; tankmen forced enemies to stop, so the splash damage from the cannon could be maximized. Toward the end, as vehicles and flying enemies became more prevalent, I found myself using the turrets more. I do wish the turrets and cannon had more distinct differences, as by the end of the game, once the tankmen became less useful, they seemed very similar.
I find a lot of what makes the game remain interesting toward the end isn't so much that it becomes harder so much as the change in strategy relies on the expectations built through previous levels. For instance, I beat the third to last level using only turrets, which from an outside perspective is a stupidly simple strategy, but becomes unintuitive within the context of previous levels requiring you to use the tankmen a lot. This hampers replayability a lot. Another balance-related issue is that the last few levels actually aren't that difficult; most of the excitement comes from the power creep on both sides as your fully upgraded towers bash away at huge damage sponges (oddly enough I was able to kill Bizarro Tom really, really fast.)
Everything outside of the mechanics is basically flawless. The graphics, animation, voices, music, etc. all look great. The voices sometimes repeat just a bit too often, but in terms of style and presentation this game looks incredibly polished and the fact that this exact game could hypothetically have been made in 2005 (during XGen Studios' golden age if that puts things into perspective) is mind-blowing.
9/10 for overall quality, enjoyability, and execution, -1 for some balance issues and lack of replayability.