Fantina's gym in Platinum (not diamond/pearl) was pretty cool. I liked the idea of the darkness, and the gym utilized it well and uniquely (despite it being similar to Brawley's gym in Generation III. It was used better in Fantina's gym imo). --- Wild Pikachu Appeared! Go Pokeball!
I'm quite fond of Sabrina's gym. The warp panels were a decent idea, and the gym itself was short enough that it didn't wear out its welcome. The best part was if you solved the "puzzle" perfectly, you didn't have to face a single unnecessary trainer if you didn't feel like it.
Opelucid in BW2 had a fairly intense feel to it. It was probably my favorite gym of 5th Gen, followed by Roxie's.
I just want to point out that the Gen 5 (at least the B/W version) Dragon gym was my most hated gym of all time. Yes, I know that RPGs tend to have larger building interiors than exteriors, I've made peace with that and can suspend my disbelief to an extent... but the B/W gym specifically was just ludicrously huge beyond all reason. B2/W2 is slightly better about it, but still obviously too big.
Then you get to the actual gym layout... massive statues of dragons which can move and bend? I don't ****ing buy that for a second. It looks fugly, the gimmick is [mentally challenged], and it was nigh-impossible to leave until you cleared at least half of the (annoying as ****) trainers out first. And when you do come back, you have to sit through a few minutes worth of watching the crappy statues slowly moving around again.
Also, I despise gyms where you can't skip trainers. I like to fight them all anyway, but I love at least having the choice... and the opportunity to heal up if one trainer proved to be particularly tough or lucky. --- Another day successfully wasted. "I need a new quote for this signature." - Me
I admit gen5 was a good step in the unique gyms but I do miss a good puzzle.
Gen 5 was a step backwards. If they are just going to lead you on a straight path, there is absolutely no point in including all those "gimmicks". They were pretty much just a medium for the developer's to show off the game's graphical capabilities, and nothing else. That's not "unique" at all, just a pretty looking straight path.
Saffron City's gym was unique. Blackthrorn's gym was unique. Nimbasa's gym was not. --- Not changing this sig until we get a new main series Tales game released on a Nintendo console in the US