"The long-lost relative we've never heard about" is of course a huge cliche for human storytelling at this point, and I guess TNG was running out of ideas at this point as they used it at least four times during the 7th season - with Troi, Data, Worf, Picard.
Out of those 4 this episode is clearly the best. As was unfortunately common at this point in the series, the story is saddled with a thoroughly banal scifi backdrop - the kind that makes you wonder if the Enterprise was the Federation's handyman.
The story with Data's mom, though, is genuinely touching if somewhat slow. The last ten or so minutes in particular are the kind that show why Brent Spiner's ostensibly emotionless character is in fact one of the deepest emotionally on the show.