Monsters has a demo - it's basically Tower Defense
A much lamer version of Tower Defense.....which is free.
bullshit

. they're two different flavors of TD, and PJM is top tier for that style of TD. replay value after getting a rainbow drops off, yeah, but getting to that point is quite a lot of fun as long as you aren't a cigarillo and use a guide. i rarely play games a second time through so it doesn't really matter to me.
i've played the flash game and i was really into the wc3 maps that the flash game ripped off, and PJM is definitely a great TD game.
it really just shows how much you know about the desktop TD game you seem to be referencing as well. to get the best score, that version is just as much 'trial and error' as PJM. it all comes down to statistics in the end and you'll eventually find there's only one real option.