This episode has one great part - the poker sequence at the beginning, which is just incredible fun to watch.
The rest is very typical 2nd-tier TNG. The Enterprise discovers Tasha Yar's long lost sister, who is the member of a gang. (Perhaps this episode was intended as a commentary on gangs - but I don't know what the commentary actually is.) Yar Jr. insinuates herself into the crew members' hearts, including Data, and then betrays them at a crucial juncture.
Overall, that merits a big shrug and probably a yawn. As with most of the weaker episodes during seasons 3 & 4, there isn't anything offensively bad here.