There are two things about "Grail" that keep it from being an average episode for me, one is the na'ka'leen feeder, the other is the potrayal of Jinxo.
The voice of the feeder is not to my taste. I'm not sure the thing should have even had a voice, to be honest. That wimpy voice it had made it seem much less threatening to me and broke the suspense of it. Some of the CGI for the feeder was pretty nice, especially for its time. For me, the best part about the whole feeder in this episode is the reactions of Londo and Vir; those are some quite funny scenes.
Poor Vir getting locked out into the hallway!
As for Jinxo, I like the character in concept, but not in execution. There's something that's just not quite there in the performance of the character that, with the character being such a major guest character this episode, deflates the episode for me. Again, in concept I like him: the fear of being cursed and staying on the station to try and prevent that curse from destroying it, but then having Aldous reveal another perspective on it that Jinxo was lucky in having escaped all the previous stations' destruction. And I like Jinxo's taking up Aldous's quest after Aldous's death. But again, there's just something in the performance that doesn't live up to the character in concept for me.
The whole bit of Sinclair's looking for a reason is brought back into the episode, which is a definite boon for the story. (Random thought of the moment: it's kinda fun to note the similar character element in David Martel, who says at the Naming Of Names ceremony that he's searching for something.)