You're right, there. pre-evolution Pokemon just don't look right in the whole game, in my opinion; at least when they come after their evolved forms, which is the case for pretty much all of them. Generation II pre-evos weren't so bad, but then they made the most pointless pre-evo in history at the dawn of Generation III; Wynaut. I ask you; why does something as nasty (as in Pointless Pokemon Alert) as Wobbuffet need a "baby" Pokemon...? o_O
As for advancing evolutions of past Pokemon; I'm none too bothered about them. Though there are some I just wonder why they were created. I'll go through a list of those I can be bothered to comment on:
Mamoswine: They could have done better with its evolution. (I, for one, didn't even know it was an evolution of Piloswine, when I first saw it) Its true that Pokemon change their appearance when they evolve, but in the case of Mamoswine, that was a change that really should have been more subtle.
Electivire:I actually like Electivire. Its one of those evolutions I've grown to like, over the time that I've owned one. The only thing I'm not too keen about are those things on its... back? I've heard they're actually tails, (apparently, in the Anime, they glow when it uses Iron Tail) but they don't really look like it...
Magmortar: Probably one of the lesser Pokemon that I like; its actually closer to dislike, though. I don't really like its design.
Yanmega: This one isn't so bad, but it does look strange, to have been an evolution of Yanma; but from looking, I did actually assume this to be a Yanma evolution, unlike the Mamoswine incident.
Glaceon & Leafeon: Without a doubt, probably two of the visually best evolutions, of a past Pokemon. Though that's coming from an Eeveelution fan. XD Eevee is probably one of the only Pokemon exempt from the rule of evolution, in the fact that there will always be evolutions of Eevee, (should they continue in Generations) until all of the types contain an -eon. Personally, I feel that this stands true to the Normal type, as well, since I've strong hopes that they'll bring out a Normal type Eeveelution, one day.
Rhypherior: Probably the one that looks the strangest. I'm not really a fan of this one, for how it looks. They kind of did a number on Rhydon, when it evolved, in their minds.
Porygon-Z: With its name, I actually think they'll start doing branch evolutions named "Porygon-X" and "Porygon-Y". but on with the Pokemon at hand, Porygon-Z is another of those I like. It looks a little strange, but that's to be expected from a virtual Pokemon, right?
Lickilicky: I really don't like Lickilicky... ._. It looks like some sort of gang boss, or something obscure, like that. Personally, I don't think Lickitung needed an evolution, if Lickilicky was the best they could come up with.
Magnezone: It looks like a flying saucer, is all I can say about it. Its a pretty drastic evolution; as with Mamoswine, but its still recognisable with the Pokemon it relates to. I'm none too fussed about it; even if people think its one of the best from D/P/P.
Probopass: Probopass is the strangest; it has to be. Visually it looks really weird, but it can't be mistaken for much of anything else, other than a Nosepass evolution. Personally, I don't think it was needed, regardless of what people say about Nosepass's stats. All I have to say to them is look at some of the evolutions; they didn't go so well for the Pokemon they evolved from, did they? *kind of looks towards Sunflora* On top of that, not every Pokemon evolves.
I think I'll leave it at that, for now. I don't really have anything else to say on the matter, other than pre-evolutions are probably the worst thing for them to keep repeatedly doing, and that advancing evolutions are always going to be up in the air. Not everyone is forced to like what others do, and likewise with dislikes.