Referring to comments by patlandness:
Well, for me, there's a huge difference. "Trials" is a fun episode whose basic premise is silly in that it's really meant for the fans. As such, contrivances don't really matter as long as the show hits the right tone and the right spirit which IMHO it does. The episode itself doesn't want to be taken seriously.
"Darmok", on the other hand, wants to be taken seriously. And that, IMHO, is why contrivances such as the ones I mentioned do matter. The more seriously a show takes it itself and wants you to take it, the more it needs to get certain just about everything right.
Episodes that deal with more serious subject matters will be scrutinized a lot more than pure fun episodes that clearly wink an eye at you and say: "This is for fun!". IMHO "Darmok" just doesn't hold up to the higher standards. Personally, I simply have a hard time taking it very seriously. I'd also add, as mentioned above, that I don't find it particularly deep in its message.