Would you mind talking about the Spinarak line if you haven't already? If you have, I'd love your thoughts on Skorupi! (And vice versa; I did some searching but I didn't see it)
Spinarak is a cute little guy! It's probably the simplest spider design we've ever gotten in Pokemon, but that's a not a bad thing. The blank-ringed eyes convey a sort of compound eye without being too literal with it, and the little fangs and random horn (following in the proud Gen 1 tradition of slapping horns onto things for no reason other than that it looks cool) add just enough detail to prevent it from being too bland. I also love the stripey legs, a feature found in many spiders.
The main draw of Spinarak is the concept of it having a second face on its abdomen. Not only does this make logical biological sense (it would confuse predators), but it also makes for a fun little theme, and increases the cuteness by 20%.
My only real nitpick with the design is that the red fangs feel a bit out-of-place; they could've easily been yellow. Then again, it ties into Ariados' radically different palette and many IRL spiders have different-colored pedipalps, so I'm willing to give it a pass.
It's also worth nothing that Spinarak had a completely different palette in general originally, sporting a mostly purple look. Ariados was also purple originally, which created more design coherency between the two stages. I'm not sure why they changed this. Maybe they thought it made them look too much like poison-types?
While it's a shame that there's little color consistency between the two, there's at least some visual consistency—the horn, the stripe and spots on the abdomen, the fangs, and the striped legs all remain. Meanwhile, the body shape has changed in a way that makes it look appropriately stronger, and its gained a really pair of false legs on the back that no other spider 'mon sports.
Unfortunately, what doesn't remain is the theme. Spinarak's most noticeable feature was its false face, so it's baffling that Aridos drops that in favor of... nothing really. Aridos is nicely designed, sure, but it doesn't really have anything specific to make it stand out. I point this out mostly because this was Aridos' beta sprite:
Most of Aridos' design has been improved from this design; the finalized design sports a much more interesting body shape that looks much more different than Spinarak's than the beta's does, and the face feels a lot more complete in the final with its thinner head and larger eyes.
However, the loss of the face on the back was honestly a travesty. Like I said, the face on Spinarak was its main theme, so using the evolution to advance the face from being a simple smiley face to a full-brown vicious pattern ala Arbok would've made the line much more memorable, and would've created a greater sense of increase between the two stages. Even the final Pokedex entries for Aridos still blatantly reference this earlier design:
If they had kept Aridos' final design but allowed it to keep the false face of the beta, the line would've been dang near perfect. As-is, they're both still enjoyable spiders—just not nearly as memorable as they could've been.
As a final side note, I could see potential in revisiting this line. I don't think a third evolution would be out of the question; maybe play back into the face theme or expand upon the false legs by giving it the ability to flip itself upside-down or rightside-up on a whim.
