Oddish is based off of a mandrake, and in addition to being nocturnal and burying itself during the day it also shrieks mandrake-style if you pull it out of the ground. I'm mostly mentioning this because the mental image of this cute little thing screaming bloody murder because someone pulled it up is hilarious.
Anyway, yeah, Oddish has a perfectly nice design. The blue body is what really makes it interesting, helping it avoid the sort of generic green grass-type motif that we see a lot. I also like that it doesn't have arms and just runs around everywhere on its two little legs.
My only nitpick is more to do with the entire line; Oddish only having green leaves makes it feel a little disconnected from Gloom and Vileplume. I would've liked to see a little of the red worked in there, maybe at the base of the leaves. That's obviously not a big deal though.
Gloom is where things really get great, as we begin to see the line's theme come into play: they're based off of corpse flowers! I.e. those giant plants that look and smell like rotting meat.
Given how many grass-types are just generic green leaves and flowers, this is an insanely cool plant to take inspiration from, and its habit of drawing in insects with its smell makes it appropriate for their poison-typing as well.
Gloom also does a good job as a middle evo; it transitions clearly, but it doesn't look like either, with ball-like petals instead of Vileplum's giant open ones, some long grass-like red leaves, and a drooling, sleepy expression that adds a ton of personality and feels fitting for a corpse flower. Also, once again, I love the non-traditional colors here.
My only nitpick is that I could've done without the arms, at least until the last evo, just because that would've been more interesting. Other than that, Gloom's pretty perfect.
Vileplume's probably my personal fav out of the line; I love being able to see the flower in full (said to be so huge it has trouble holding itself up, a nod to how rafflesias have the largest flowers of any plant. The colors still look great, and maybe it's just my imagination, but I love how vaguely threatening it looks, like it's trying to look friendly but is secretly planning to stun spore you out of existence.
My only real complaint is that, while the expression is fun if you interpret it that way, it doesn't really make sense to go from Oddish's face to Gloom's face only to go right back to Oddish's face with Vileplume. I feel like either Gloom should've had Vileplume's face and vice-versa, thus adding a sense of progression, or Vileplume should've had a different face entirely. Regardless, it works perfectly as a final evo, and it still embraces its corpse-flowery nature to its fullest instead of just being a generic flower.
I mean, Bellossom's not really bad; I don't even have much to critique about it, other than maybe the length and thickness of the arms is a bit off, but... really? We really needed to add a split evo to this line that throws out the one thing the original line had going for it?
I mean, to be fair, I kind of see what they were going for; it evolves via sun stone, and goes from night-flowering to day-flowering, from vaguely malicious and kind of gross to generic and pleasant. There's definitely people out there that would find Bellossom more appealing to them personally, even if I don't.
However, I think my main problem with Bellossom is that it really, really does not fit with the original line visually. I may not care for Gallade that much, but at least I can see how Kirlia evolves into both it and Gardevoir, and how it fits with the rest of the line.
But Bellossom? Bellossom feels like a completely separate design that was tacked onto the Oddish line during development (which to be fair, it very well could have been). The colors are completely different; gone are Oddish's pleasant blues in favor of yellows and greens. The eyes are much more detailed and different than the rest of the line's simple dot eyes. In fact, the only single thing I can see that connects it to everything else is the shape of the flowers on the head, and that's not much.
What's particularly weird about the colors is that some early art shows it did have bluish skin originally, and I don't know why they changed it (even the original shiny had blue skin before it was randomly changed to lavender):
At the end of the day, Bellossom just feels like it shouldn't evolve from Gloom, or even be connected to the rest of the line. It's not bad in and of itself, but it adds nothing; and at the end of the day, if I want a humanoid grass-type wearing a dress with a flower, I'll take Lilligant any day of the week.
Overall: Oddish is cute, and I adore the colors and corpse-flower theme of Gloom and Vileplume. Bellossom, meanwhile, is fine but doesn't fit with the rest of the line, and is much more generic. Still, the original trio are still some great and refreshing grass-types.
Also, enjoy this oddly ominous card art of an Oddish looking like it just blew up a town without remorse:
