As great as Gates McFadden is to look at, the Beverly Crusher-centered episodes are often pure crap (with the exceptions of "The High Ground" and "Attached", but they focused the dynamic between her and Picard). The character just never seemed all that interesting. All we knew about her was that her late husband was a close friend and confidant of Picard and that her son, Wesley, served as "Acting Ensign" on the Enterprise for some time.
"Sub Rosa" was an attempt to focus on her family's backstory. That had already been done with virtually everyone else in the cast (even Data), but they attempted to throw a parasitic, womanizing "family ghost" into the mix. If this is what it took to give Beverly an interesting past, it didn't work.
We never see the character of the grandmother, so we ultimately don't sympathize with her. There is no chemistry between McFadden and Duncan Regehr, who establishes himself as creepy from the outset, destroying his effectiveness as a character. The only bright spot is the reliable character actor Shay Duffin as the gardener, but his screen time is minimal.
This episode has no bearing on the series as it is, and there's no amazing dialogue, convincing acting (except for Duffin), or character development. Skip it.