The TNG episode "Darmok" features what I believe to be an animal that's either trapped, somehow in an alternate dimension that is sometimes allowed to come through and strike. Or ... it could be an animal that's somehow able to use and focus energy around itself for stealth and camouflage. However, it does stand upright, seemingly on two legs and has two arms, which it uses to fight, as a Man would. So is it an intelligence? Or just a kind of energy ape with a horned frill? Despite being shown briefly, TNG shelled out the bucks for that suit.'
VOY had some really stupid-looking CGI this and that's, from Species 8472 to some flying tentacles to an incredibly lame cave serpent ... and you just look at these things and cringe, going, "why did they bother, when they knew they didn't have the money for it, in the first place?"
Then, you've got the other extreme, as with Kruge's dog in THE SEARCH for SPOCK, who's nothing more than just a cool addition, and that's all. The coolest thing about it is that it's just there for the audience. To help sell the environment, or to underscore a character trait, or something that really doesn't need to go to that extreme. But they do it anyway, even though it wasn't free and people love that kind of thing. They appreciate the imagination and effort that goes into something like that and it's not even necessary. Across the board, really, I think that's what the animals mean to me, in STAR TREK. Just that little extra effort to say, how cool is that, huh? But when it's called on to do a great deal and it's not up to it, like CGI that clearly wasn't budgeted, then it's like ... you should've just saved yourself the money. I didn't need to see that ...