With regards to the starters especially, I imagine a reason for disgruntlement is that the middle Pokemon lack the cuteness of the starters themselves and the power of their final forms. They're essentially the teenagers of Pokemon: gangly, pimply, unsure of themselves and their bodies.
That's actually a good definition for the "middle stages" of starter Pokemon lines. XD
Yeah...I've always viewed the middle stages as a bit...offset from the other two stages. It feels like the first and third stages were designed first, and the middle stage is simply a filler species or an afterthought; something to bridge the gap between the first and third stages. This is more evident, IMO, with Combusken, Marshtomp, Grovyle (to an extent), Charmeleon, Monferno, Prinplup, Grotle, Pignite, and Servine. Save for Grovyle, Charmeleon, and Pignite, the other names sound sort of...uninspired. I mean, with Grotle, they used the same prefix of Generation 3's middle stage,
Grovyle. Monferno takes the other part of "inferno" that Infernape didn't use, and Prinplup isn't all that different from Piplup. Servine and Pignite partially sound like weak attempts at portmanteau-ing different words...
Generations 1 and 2 don't seem to have the middle stages clash with the other stages as much as other Generations do...
I don't know...it's just that these guys look a bit funky with unnecessary details compared to their pre-evolutions and evolutions... I guess it's just down to opinion. It's a shame that these stages get shafted so much...typically, you start with the
first stage, so that's probably the more memorable and nostalgic one you fondly think back on, while you pretty much go through the rest of the Pokemon's life in its final stage where maximum growth is to be achieved, so people are likely to be much more accustomed to the final stages in the games... The middle stages are kind of like a temporary puberty or growth spurt... :\
Porygon2 is a mid-staged pokémon that's often regarded as more useful in competitive play then its evolution. Even before Evolite was implemented, Porygon2 saw use comparable with Porygon-Z in early DP, due to the fact that it not only had higher defenses then Porygon-Z, but it was also the bulkiest pokémon with Trace available, as Porygon-Z always loses Trace in place of Adaptability upon evolving. Combining Trace with it's respectable defenses and offenses, ability to use Recover plus electric and ice attacks, Porygon2 could take down things such as Salamance, Gyrados, and Heatran with ease, making it highly coveted, until Hitmonlee version released Outrage to Mence, rendering Porygon2 much less effective at countering what it was most needed to. This combined with crazy issues eventually caused it to fall back to the depths of being a situational pokémon only useful for setting up Trick-Room...Until Stunfisk and White came out.
Rising from formally being (quite literally) considered obsolete to one of the best defensive pokémon in the Blanket, Evolite gave Porygon2 the exact thing it needed to be able to handle Salamence again, and not only that either. With Trace and its boosted defenses, Porygon2 can also fight toe-to-toe with Hydreigon, Garchomp, Rayquaza (Try and use Porygon-Z for that, heh) and more! As Trick-Room also gained recognition as a viable strategy with the help of a certain green blob, Porygon2 can also show off its utility as a support pokémon, using its quirky move-pool to the best of its abilities, with an improved Magic Coat and recovery abilities being its main points.
On the converse, Porygon-Z is actually falling bellow Porygon2's usage level from the increased usage of fighting types along with the introduction of Genosect, a pokémon with Download which though hits somewhat lighter, has a much more stable defensive type along with a higher speed. Whether Porygon-Z will see increased usage for whatever reason remains to be seen.
Ironically, one can say that Porygon-Z did in fact make Porygon2 a better pokémon, even if it did so through rather indirect means.
I heard that Porygon-2 was at times more formidable than Porygon-Z, but I didn't know it was more skilled than its evo to the point where it can challenge
Rayquaza. 0_0 I'll still likely evolve Porygon-2 to Porygon-Z, but the fact that Porygon-2 is a threat in itself is pretty intriguing...
My Metapod named 'Penis' used Harden, rendering the OP's point invalid.
Noob out.
Eww...
In any case, there are several "middle-stage" Pokemon I enjoy; it's just when the middle stage looks a bit disconnected from its pre-evo and evo that I view it a bit differently...