I have to say I don't like it. The relentless pressure isn't fun, the lack of an ending isn't fun (in Element TD, I could say "I almost made it that time!"... here, I can only say "Well, level 54 that time"), the tower and upgrade options don't have any thrills and chills (research in Element TD added some of that), and the format of it makes it so that there really aren't any great placement decisions. The best placements are trivially obvious, and any placement is almost as good. So the strategy is gone, the rewards are gone, the interest-earning challenge is gone, and it adds a crushing sense of impending doom, and an absence of feeling of success. Nothing good about that. The 9 levels of upgrades also make upgrading seem really uninteresting. A few powerful ones is much more exciting.

So a huge disappointment over something I was really excited about. I will be going back to play Element TD, but not this game.

Now if you want good, how about this other one I've been playing lately: DesktopTD

It adds something I had forgotten about in TDs since Art Defense (or whatever that gallery one was called) - making mazes and blocking monsters. It also has very powerful and interesting upgrades - the final upgrade for each tower converts it into a super tower of some sort (for a lot of money). Most viciously, the flying monsters in this one comprehend what flying means and actually go right straight across the map. Watch out for them!
 

I think you are right. I've played it a few times, but it doesn't have quite the compelling pull that the original did.

And I tried Desktop TD. It was really fun. That one could get REALLY addictive.