The music, the screenplay, the direction and the camera work & scene layout are all pretty good. But I think the puppets and their animation lack the expressiveness to really make it work well.

There is none of the brilliant animation that can be seen in Roman Kachanov's puppet films. And no wonder, considering how rushed this production was. In the article linked above, Migunov wrote about how the team of Grigoriy Lomidze, which was working with live-action puppets and easily meeting all the deadlines (and hadn't had to set up an entire new production line), was getting all the praise from management.

He had tons of trouble getting a cast of the main character:

Besides the miniature and complex molds, we had to ensure the casting surface was flawless, as straightening was out of the question. And casting after casting failed. (We tried to find a way to manufacture rubber toys in a factory, but that required a metal mold for vulcanization, which was completely beyond our capabilities! So our only option was latex!)

I gradually began to get nervous. Deadlines were pressing, management was furious, and the workshop couldn't cope.

[...]

But finally, a more or less high-quality casting was achieved.
With bated breath, I began installation. And discovered I had miscalculated the shrinkage of the latex. It turns out that as it dries, it shrinks significantly over time: it shrinks almost twice as much. Who could have foreseen this? The mold was made with some allowance. But for the allowance to be so large...

I almost lost it. Somehow, by filing down the pins and shortening the frame levers, I managed to dress my hero. What's more, I even managed to insert a special mimic mechanism into the head, activated by a hidden screw on the back of the head. With great difficulty, the hero was born. Another problem emerged: latex can't be painted. Oil eats away at it. Gouache crumbles. Only special makeup made from pig fat or spermaceti has no effect on latex. But then again - it smears when touched.... Well, could there be a better cure for sleep?

I turned blue and my heart began to skip beats. [Studio director] Sinitsyn, as if sensing this, called me every day, several times a day, constantly taunting me with obscenities. One night (though later, at the end of filming), he got in a full charge. Burlakov - the production director of my picture - didn't have time to cut the line, but rushed to it when he realized I was about to recite my own piece. The recitation was impressive. Later, when I finished and handed in the picture, Sinitsyn told me he thought he'd dreamed the whole thing...

He was also unhappy about the animator:

Vadim Dolgikh was assigned to me - a very mediocre animator, to say the least. Lazy and lacking initiative, he brought no benefit to the film. And if he did contribute anything, it was only quantitative, but not qualitative. He was not subtle, not intuitive, not artistic. I tried to persuade Boris Dyozhkin to try moving things around. But, first of all, there was nothing to move yet. And, having familiarized himself with the armature (the spare one), he fiddled with it a little, apparently enjoying himself, but for some reason eluded any serious work.