I thought the Pah Wraiths storyline could have been great. The Assignment, the Wraiths' first appearance might be the scariest episode to me in all of Star Trek. Also, Gul Dukat's interest in the Wraiths actually fit perfectly with his character, desperately wanting to be loved by the Bajoran people. However, it was only a subplot that could have succeeded if it was the main storyline, not playing second fiddle to the Dominion War. You either have to go all out with animatronic/cgi Pah Wraith demons or not bother at all.