Adam is one of those stories that works really well but does rely on science fiction tropes pretty heavily. Reviewers from earlier have mentioned how Doctor Who has even covered this idea of an outsider messing with people's memories and getting everyone to think they've always been there, but the sticking point for me is that two other franchises have done this idea really well before and since. In the 90s, Star Trek: TNG called Conundrum, which explores this idea really well and frankly, better than Torchwood. Rick and Morty also took this idea to the extreme in their episode Total Rickall, which took this concept to the extreme and had a lot of fun with the idea using "memory parasites."

Torchwood has Adam, which isn't very original in its basic premise but does get creative in making it that particular brand of Torchwood tragic. It's not just sad events, but sad events that feel like they just pile on to our characters. Adam himself is pretty boring but they do have fun with his effect on the main cast like Tosh and Gwen. The big show-stopper is Jack, who has to compromise away his scant happy memories of his early family life. It underlies the tragedy of his immortality - the longer he goes, the more and more those early life memories (and other key parts of him) are likely to be compromised away.

All told I consider this episode largely impressive and well done. A good example of Series Two of Torchwood having a stronger repertoire of episodes, and fewer (if any) outright abominations. Also a good episode for carrying the larger story arc of this series, building out hints of Gray and what might be coming quite nicely.