1. You have to have a square logo. If it's landscape, you're out of luck because you have to make it tiny to fit in the square box and it looks stupid (there's tonnes of space either side and all around!). Why does it need to be square in a horizontal layout, and then SO small? This is somewhat of a showstopper.
2. You can't move blocks, so if you resize text and it overlaps you can't do anything about it. Simply being able to move graphic and text blocks should be a given.
3. Generally limited text styling. Can't choose font, italics, etc. (edit: to be fair, some templates do, some don't.)
4. Can't go back and re-crop images, have to re-upload! And the re-sizing is clunky.
5. Backgrounds?
6. Music selection requires a filter for genre and mood. I'm getting Christmas tracks at the top of the list and it isn't Christmas.
7. Music doesn't fade out, but cuts out abruptly.
8. So far everything I've generated requires further editing.

Having said that, it does make some fantastic animations. And the price point is pretty good. But honestly addressing these issues would make it SO much more versatile, and add very little complexity. Right now it's probably worth more like 3.5 tacos, but could easily be 4.5.