This episode has an interesting premise, but poor execution. They quickly retconned the whole Trill symbiote idea since it was started on TNG, it started as the symbiote being the conscious one and the body just being the body, but it would seem this episode retcons it again. Instead of being a partnership, the body now is the conscious one, and the symbiote worm thing just gives you memories, enhances your IQ. I think it's a little early in DS9 to be totally rewriting your fictional rules.
The new Dax is happy to be a villain, although it's not clear he's even conscious. He's maybe just a dumb space slug along for the ride. The new Dax also immediately betrays and turns on his hot girlfriend, even a sociopath might take more than five minutes to dispose of the only person who cares about him. It's so, SO, terribly convenient for the plot.
It would be better for this episode to have been deleted from the show's episode list.