I actually like the idea of the Caitian, if not the visual design Cryptic went with. The Caitian/Ferasan/Kzinti/Lyran/Mirak species group represented a culture and sentience very different from the typical Trek norm. Like the Gorn, they have the potential to be something genuinely alien. Their mindsets derived from a primarily predatory biology, rather than the more opportunistic omnivorous biology that presumably lead to the roughly fifteen hojillion "humans with funny bumps on their heads" species that populate the galaxy. It's a fun viewpoint to explore.

I think that the race would be much much less "stupid" if the model designs weren't just head-swapped humans with tails and fur. Give them a digitigrade model with a different posture and heads that look more generically "big predator" and less "sentient tabby housecat" and I think folks would like them more.

In no particular order:

Kazon -- they were just silly. Not the silliest, but it was just comical to see them manning the bridge of Voyager.

Bajorans -- I wanted to like them because of their history, but their religion was weird and just about every bajoran character was stereotyped into being angry/mood person who hated all cardassians. It got old after Ro Laren.

Andorians -- their antennas and white hair look dorky to me. That's all.

Trill -- they're just weird. It was super bizarre in TNG and it got only slightly better in DS9. Dax didn't help things for me, because I never liked her anyway. I also just really dislike their name; it makes them sound like fairies or something.

Betazoid -- never liked them mainly again because of character association. I wasn't a huge fan of Troi (she pretty much only ever stated the obvious and/or flirted with Riker), her mother gave me the creeps, and the only other major betazoid character I can think of was a serial killer. And, naked weddings? I didn't need that picture of Riker in my head during Nemesis.

bonus: not really a species, but have you noticed how most admirals in Trek are jerks and/or turn out to be evil? Whenever I see an admiral show up in an episode I'm instantly suspicious.

I agree. They need to look more feline. A semi-erect posture would be an easy solution. But all the canon Caitians had an erect posture.

I agree with this.

Considering they probably ran out of the Caretaker's energy reserves a good while before Voyager got back to the Alpha quadrant, they pretty much failed at that, as well.

While I wouldn't say I hate them, the Ocampa's super-short lives and single-time reproductive "strategy" (probably genetically engineered by the Caretaker) seemed to be more along the lines of a way for the species to be "gently" allowed to go extinct over a couple centuries.

...wow, when you put it like that, the Caretaker screwed up pretty bad.