I agree that Visionary
is an average episode. It has it's good moments (O'Brien seeing himself die, the introduction of the dart board and the Romulans figuring out that Odo has feelings for Kira - not to mention Odo's reaction to that), but overall it really does feel like a TNG episode.
The problem is that it's a tech heavy, high concept sci-fi story. That simply isn't what DS9 is all about. TNG and VOY are more about the high concept sci-fi stuff while DS9 is more of character based show - which is why the good parts of this one revolve around the character interactions.