This concept worked surprisingly well. I'm surprised this thread hasn't gotten more replies.
I liked the combination of chess rules with turn-based tactical combat. Much of the strategy came down to attacking your opponent from squares where they couldn't attack you back. This made for some interesting strategies that wouldn't show up in standard chess. Knights, for example, can attack anyone without fear of being counterattacked (but any other piece can do the same to them). Bishops and Rooks are ideal for taking each other out. Delivering the first strike is also very important, which makes the Queen especially useful.
Of course, as in most TBT games, the tried and true strategy of focusing fire is usually all that is needed for victory. Usually, the optimal strategy is using the Queen to chase every enemy piece on the board while ignoring your other pieces entirely.
Sadly, the AI isn't as good as it could be, which removes some of the depth of the game. If you can win by mindlessly beating on your opponent, advanced strategies aren't really necessary. The mediocre AI is understandable given the competition's time constraints, though, and in fact is quite good, considering.
The power-ups add a nice twist by encouraging movement rather than just beating on each other. Though it was a bit annoying to have my Queen demoted to a Bishop unexpectedly. Why not give the Queen an attack boost (or something similar) when acquiring the item?
I notice that, unlike normal chess, killing the king is not the key to victory. I wonder if changing this would make the game more interesting. Stalling (by constantly running away) is incredibly easy in this game, with the right pieces, and unless one player is dominating the other, the game could easily reach a stale-mate. At least, it would, if the AI knew what was good for it.
Thankfully, the AI spends most of its time defending. Defending is a worthless option, since running away can usually prevent being hit at all. Even if running away is impossible, defending will only delay the inevitable, and will never put you in a superior position.
The game's graphics are a major weak point. The colors choices are really poor, and hurt the eyes after a while.
The game's other problem is becoming too repetitive. There's no real variation to differentiate between battles, and the game gets boring a bit too quickly.
I liked the quotes between battles. A few made me laugh out loud. Made me wonder what happened to all those pawns, though.
All in all, though, this was a unique and enjoyable tactical game. I'd like to see more games like this get made.