I have a more mixed opinion of the Gen 5 sprites, namely that the concept of them was cool and a nice bridge from static 2D sprites to more fully animated 3D models, and in hindsight they do look janky.
That said, my opinion is more that they highlight a general trend of Pokemon: they work really well with anything that was introduced in Black and White, but when applied to old-gen Pokemon they look pretty bad because old-gen Pokemon were simply not made to be shown with that level of movement in mind design-wise.
With the Pokemon introduced in the gen itself, however, there are some good designs build around the animated sprites.
Usually the starters are the ones who shine the most with the particular design quirks of the generation and the sprites/models of that game, and in this case the final form Unova starters shine with their personalities poking through. Serperior not taking its opponent seriously, Emboar pumping itself up for combat, and Samurott having an imposing presence striking fear through its foes.
But then there are different flavors of sprites, particularly Pokemon who have design features that pop with the looping animations:
Things like Zebstrika and Blitzle flashing yellow at times, Cofagrigus retracting into its coffin and back, or Ferroseed's spinning and Ferrothorn clinging to a ceiling are things that couldn't be conveyed with a static sprite.
More prime examples. Seismitoad's vibrations, or Eelektross's spots glowing.
Then there's cases where the animated sprites showcase expression and personality.
The evolved elemental monkeys in particular. While the Pans look pretty good in the BW animated sprites, the Simis showcase unique personality traits through these animations. Simisage's rougher, outgoing, enthusiastic personality with its thumbs up and its jumpiness reflecting a more punk like personality, Simisear's easygoing and carefree demeanor, and Simipour's gentle and friendly, yet smug face with it constantly waving hello.
Scraggy and Scrafty are another major highlight. Scraggy's "baggy pants" shine as a major design feature, but Scrafty's rough, hooligan, and abrasive personality shine here.
Bouffalant getting ready to charge.
Escavalier jousting its two lances, or Accelgor showing its ninja-like grace while also standing cross-armed.
One of the most masterfully designed Gen 5 families. The animated sprites show off the Sandile line's personality well: Krokorok is one of the coolest middle stages, with its cross-armed pose and general personality shining through, though Krookodile's more aggressive personality also shines.
And next, there's....KLINKLANG
The Klink line, while often clowned upon, is a line that really shines with BW's animated sprites: the looping motion shines with their gears spinning around in constant motion, and the speed at which they turn is also believable based on how many gears they have. This line is one of the few Gen 5 lines that transitioned well to 3D since it's in constant motion in a way that still works.
And then there's Hydreigon
Hydreigon's constant head-biting with its two hand-heads is something that really works here.
And lastly, there's the cover legendaries:
The glowing tails of them shine here.
Now granted, I agree everything else looked kinda ass in BW and BW2. But the Gen 5 roster in particular brought some unique designs that shined with these animated sprites. These designs wouldn't have worked in the older gens' static sprites, and they're designed in such a way where not all of them fully transitioned well into the 3D era. The 3D models have their own strengths, and some of these design strengths still shone through, but these designs had something unique about them that worked in BW and BW2.
They contrast the older gens' static sprites, which have aged more gracefully overall, but the mons designed in those days were designed to look good in stationary poses that could be drawn. The mons from later gens were designed around motion selectively that shined at different points, whether a design feature that popped while attacking, dynamic facial expressions (Amie/Refresh), a clean walking/running animation, or design features and details that could only be seen looking at the Pokemon from all sides of the camera.
