Ah, missed this thread somehow, my impressions from the demo thread:
We have played around 10 lvls already, so here are our first coop impressions:
The warping was toned down significantly and now happens only when you are stretching the screen beyond its size,
so the coop is now playable.
But the screen size is still the same small without any zoom-out option, so its harder to control the map. I guess it is by design, but it makes thing harder and warping inevitable few times per level.
3D nature of maps adds further complexity, sometime in a good way (use elevation to increase effective range of yout towers), sometimes in a bad way ( need to go around and jump like crazy to get from A to B.)
There is no 4-player local coop ( kids are so :( ) , no coop rankings, a first person view is also disabled in coop as it was in the demo. There are only 2 difficulties so far, so I have no idea how to get third rainbow for a stage.
It also goes pretty difficult pretty fast, but this is probably good, given I do not see that much levels to play.
Overall, we are still enjoying it and will play through with my wife, but I do not see much long term coop value, especially with the rankings missing.