this has potential to be a good game. making your own side scroller would be a fun thing to do, especially if you could share them with friends. Maybe if you worked on the interface a little, making it easier to navigate the menues and place monsters and traps. also i would add a little polish, for example allow the players to animate a little 8-bit character to use. the more you add to a game like this the better it will be (as long as its user friendly)
i think this is one of the best developed flash games i have ever played ^_^ its something i would expect to see an a handheld. If i did, it would be a buy no doubt lol.