Such potential, wasted...
The graphics where good, I liked that several kinda of enemies showed up in each wave, the attack patterns and ability to rotate 'towers' was... at least a stab at being unique... so why did the game feel so boring?
Well, one problem I had was how the money you didn't spend the last wave was most of your money for the next wave. It discouraged innovation and fun, emphasizing following the minimum amount for the "formula" to work.
Also, with only four towers and no customization, the game felt pretty shallow compared to several recent versions of tower defense... actually, it's the shallowest I've personally played, although I'm sure there's worse out there. Pretty short, too... I'm fairly sure it had around 20 enemies max, while most tower games I've seen have easily twice that, if not more.
Also, the fact that you could re-rotate a 'tower' /once/ was slightly irksome. Basically only a useful tactic versus bosses... and the only spell in the game also was only useful against bosses. The regular enemies where just the basic "watch the computer kill itself" fare, and the bosses where kind of pushovers after being poisoned. The minibosses in the last two levels where a nice touch, but... a bit too little too late.
So, all in all... it's a good start. A very good start. Unfortunately, it falls flat in the actual execution. Here's hoping for an Ultimate Defense 2 with considerably better gameplay and depth.