It's got potential, but needs a lot of work.
The game has potential. The major problem which completely destroys it at this point is the game economy and balance. The cost to benefit ratios are completely whacked, which renders a majority of the "advanced" buildings and research completely useless in both the long and short runs. You'll either be long dead or too well off before any research pays off. As it stands, the majority of the "better" weapons are too costly to warrant their use. You are usually better off buying multiples of the lowest end weaponry. The building cost scale up only adds to the imbalance, which in order to support the defense weaponry you'll be completely bled dry of money and scraping by. This of course isn't helped by the fast the rate at which enemies appear and the rate they scale up in difficultly compounds all the previous issues.
Again the game has potential, but the author needs to sit down and do the math. The only way these kind of games work is by carefully tweaking the benefit/cost ratios in order to make it stuff worth buying. Also the enemy waves need to get more difficult at a rate that is feasible for the diligent player to be able to keep up.
Another issue is performance, but I can't completely attribute that to the author, but more of an issue with inefficient design and implementation of Flash.