The following made sense to me (please keep in mind that I am primarily an in-game trainer, who doesn't play competitively);
Roserade- let's face it, the thing's a grass goddess. Great stats and a Special Sludge Bomb have made it a real contender- and I'll definitely be using one.
Eteboss- just because Aipom needed an evolution. It's still hardly a revolutionary pokemon, but it has a lot more potential now. And it helps to have a Pickup pokemon that's actually strong enough to use in your ingame team.
Muumajii/Donkarasu- both huge improvements on older pokemon, and I'm sure that I'll be using both at some point
Munchlax- contributes a few useful moves to Snorlax, which is always cool
Weavile- great stats, and couldn't have come in a better generation with the change in the physical/special system. I even think Sneasel would have become a bit more usuable even without its evolution
Jibacoil- Magneton was already a good pokemon, and now it's a bit better. No reason to complain there.
Dosaidon- Rhydon already rocked, but the extra stats just made it so much better. Its physical prowess is one of the very best in the game.
Mojanbo- Tangela useful? Sounds good to me.
Elekible and Buuburn- maybe if Thunderpunch wasn't now physical Elekible wouldn't be as useful, but both rock. Let's face it, they made two average pokemon much better.
Togekiss- FUDGE YEAH!!! This was completely needed for our Togetic.
Megayanma- as several strong Bug Attacks are now Special, it helps to have a Bug type with such high special attack (highest for its type?), and its abilities can both be very useful in battle
Leafia and Glacia- just to round the Eevee family off, and they're both pretty good in their respective fields. And it finally shuts a lot of people up having a Grass-type Eevee
Glion- good, but doesn't have enough moves that make use of its amazing defense
Manmuu- made Piloswine far more useful, and that attack sure is handsome
PorygonZ- now that we have several special normal-type attacks, why not have a Normal type with god-like special attack? And I do think a third Porygon was a nice addition to the line, and with Adaptive as an ability them Normal attacks are even better
Erureido- That shut everybody up! I like how we've got a stable physically-based psychic type, and it looks amazing. I'll be using it.
Dainoosu- YES!!! That thing is a king tank, and it looks so contemporary!
Yonowaaru- Don't dispute a good thing. It's an even better tank, it's a bit faster, and it has some sturdier attack strength. What the hell's not to like?
On the other hand, the following are not necessary;
Riishan- contributes nothing of use to Chimecho
Bonsly and Mime Jr- contribute nothing to their evolved forms, but I like them either way, and I always thought prevos would make sense for Sudowoodo and Mr Mime
Subomi, Pinpuku and Tamanta- also useless to their evolutions
Berberuto- Not enough of an improvement on a weak pokemon. I guess it gives Lickitung fans a chance to use it to a bit more effect, but I don't care for it
Yukimenoko- A Glalie evolution would actually be a lot more useful. Its speed is good, but not good enough to make it uniquely strong
ChaosMage Out