I must confess... for all my complaints of unoriginality in the first half of the Unova dex, the design conceptual thinking of Gen V keeps growing on me. They did a lot of things in the evolution department with Gen V that they haven't really done before or since, or at least not to the same extent. It's as if they went back to previous generations and asked themselves "What worked before? What should we do again? How can we expand on those ideas instead of inventing something new for the sake of inventing something new?"
First of all, the two flavours of regional bugs. Both a little late to evolve, both decently powerful. And neither of them were moths or butterflies. After four generations of bugs being fully evolved by level 20, or just hopeless failures competitively, it was refreshing to see some that could actually hold their own for at least the first half of the adventure (and a fair bit longer, with Hidden Abilities).
Lillipup in general is an undeappreciated Pokémon. It is an early Normal-type with an evolutionary curve not like an early rodent, but like a starter (evolves at levels 16 and 32). It is only available in the early-game, and not shoved down our throats later on like certain other early-route Normal-types (here's looking at Hoenn, Sinnoh, and especially Alola). But it can hold its own throughout the entire game, with a wide movepool and useful stats and abilities. It's as if the designers added a fourth starter Pokémon. Sinnoh kind of did that too with Shinx, but Luxray was held back by a more single-tracked and less powerful movepool.
Gigalith and Conkeldurr might be thinly veiled imitations of Golem and Machamp, but I appreciate that they reach their final forms via straight-up, no-items, no-fuzz trading.
The three elemental monkeys can generally be regarded as six buckets of crud, but at least they gave new purpose to the "traditional" evolution stones, with some help from Eelektrik. The Fire and Thunder Stones had not interacted with any new Pokémon after Gen I, while two Gen III designs utilized the Water and Leaf Stones (Lombre and Nuzleaf). Nice to see more Pokémon evolving using the stones specifically designed to evolve Pokémon.
Solosis, Gothita, Vanillite, and Klink are mid-game Pokémon that evolve twice. But their amazing little trick is how late the first form is obtained, but you still get to use all three stages through the adventure. They reach their second stage some ten levels after their maximum encounter level, and their final stage 10-12 levels after that. Contrast earlier mid-game three-stage-types like Gastly and Poliwag, which evolved pretty much immediately after capture, and then again via some more labourious mehod such as evolution stones or trading. Also, Vanillite is an actual mid-game Ice-type that evolves twice, with a decent BST and focus on Sp.Atk. It's the only regular Ice-type that makes an actual effort to be useable an interesting in-game.
Axew is a really powerful Dragon-type found in an optional side dungeon. Great concept! Being a non-pseudo-legendary Dragon-type is also pretty cool.
The Litwick family also brings back an evolution stone, this time the Dusk Stone from Gen IV. Other than that, there's also Munna bringing back the Moon Stone (unused since Gen III, Skitty), Cottonee/Petilil give purpose to the Sun Stone (unused since Gen II, Bellossom/Sunflora), and Minccino utilizes the Shiny Stone (introduced in Gen IV). Gen V made sure to remember and re-use all the evolution stones, after Game Freak made a habit of introducing new ones in Gen IV rather than re-using the existing ones.
Pawniard, Rufflet and Vullaby prove that two-stage evolutions can arrive late in the game and still be evolved via level-up, without it happening immediately after capture (shout-out to Bergmite, which can't be found in the wild below its evolutionary level). Late-game Pokémon need not be locked into trade, evolutionary stones, obscure items, or locations. Level-up evolution works even if it happens only once and late in the game. Whether or not they were successful or useable in-game with this concept, I don't know (didn't use them myself), but at least they made the attempt. They are introduced late in the game and evolve via level-up, but they follow the level curve and the base form may be used for a few levels before evolving. Other games solve the issue by putting late-game introductions way below the level curve (Larvitar, Bagon, Jangmo-o), or refrain from introducing new Pokémon that can evolve by level-up late in the game at all (Poni Island except Jangmo-o, Victory Road in general). This method does, however, mean that Bisharp, Braviary and Mandibuzz will always be very late-game Pokémon in future games, barring exceptional underlevelled encounters like in BW2. There's no catching, say, a Rufflet around Gym 4 and have it evolve by Gym 6.
Deino and Larvesta, while not particularly good in-game Pokémon, take the "late bloomer" concept to its logical extreme, not reaching their final forms until around level 60. Still, they hold on to plain and simple level-up evolution; instead of obscure, late-game items (shout-out to Sneasel), or requiring you to trade.
And in general, Gen V contains a lot of what I like to call ATEFs. Atypical, Three-stage Evolution Families. Pokémon that evolve twice, that are not starters, early-game bugs/birds or pseudo-legendaries. Gen IV had a single ATEF in the Shinx family. Gen VI had two; Flabébé's and Honedge's families. Gen VII also has two; Bounsweet and Cosmog (and the latter is debatable as it's unlike any other evolutionary family). But Gen V? 13. That's more than Gen III, IV, VI and VII put together. Although in fariness, Gen IV created 10 cross-gen ATEFs by introducing third members to previous-gen families. But still, ATEFs are a rarity nowadays, so to look back to Gen V and see the huge number of "atypical" three-stage lines is kind of impressive.
So yeah, Gen V had a lot of good ideas conceptually. By contrast, I don't think gens VI and VII were as creative, they felt more restricted in their Pokémon design and selection. They had some good ideas, of course, but Gen V did a lot of things way better than the 3DS generations of Pokémon did.