Put simply, for me it's the music and the wayyy too rapid movement that brings, well many of these animations down for me a lot.
But please don't get this wrong, still i love almost every single animation and work they put in, some of it is my favorite work of all time ever! Like you said, double dick made me rank this one much higher!
A few more frames in every anim really would enhance every vid though imo and i'd be more than willing to wait an extra week or 2 for just that.
Yeah, this is definitely the overall problem with Nyakumi (and MMD/MMD-adjacent 3d content as a whole), particularly with shorter videos.
The break-neck pacing, trying to cram 10-20 different positions and random-ass angles into a 2-3 minute video detracts from the final product. Especially when so many of the positions/angles are half-baked in an attempt to maintain some semblance of originality.
On the complete opposite end of the spectrum you've got 3d artists like Aanix, Meis3D or Rentegra; yes, their content takes fucking AGES to produce, but there's genuinely astounding attention to detail and an impressive amount of work goes into their compositions and craft. Wouldn't want Nya going to that extreme, but just taking a wee bit more time for a cohesive video would be a treat.
As you said: I enjoy the content they produce, and the level of effort doesn't go unnoticed, I'd just love to see a little more time go in to work out the pacing.