Great
The concept it absolutely amazing, I really enjoyed it.
But even though it's mindlessly addicting, it could use a little more variety, both on the upgrade part and in the actual gameplay, it was really fun, but I couldn't help but feel that all the levels were almost exactly the same. The only thing that made me hold on through the whole thing was making me feel good about myself by getting all the cups. The enemys never tried anything new, and they all pretty much would kill themselves excluding one or twp, before I would even get to them. So, pretty much, I think you could make it more of a challenge, spend more time on level design, and work out the little gameplay glitches, and you would have an amazing game.
By the way, big time game developers find their success in listening to their criticizers, try not to get worked up about what people say, because if you get past just wanting to be pissed about it, and take what they say into account, you'll have incredibly enjoyable games as an end product.