I bought this game too entirely because I am a fan of the BBC show.
I think if you are going into it looking for a "Sherlock" experience, then you will get the most value out of it. This is because the game features numerous original clips acted by the original cast of the show and plays to the mythos of the show itself. Judging on this criteria, this game is absolutely superior to most of the so-called tie-in game to existing television or movie franchise.
As a game itself, judging on its own ground, the competitive mechanics are terrible and the rationale for level-up system makes no sense.
1. The game urges you to reach a high-score by playing the case as fast as possible. However, it is all too easy to "cheat" by replaying the fixed elements of the case once you know the answers because you have solved it previously. On the other hand, the random nature of the mini-games (Mastermind clone, for example) means that you cannot win the game by skills alone. Thus, a winning score on the leaderboard means nothing, neither representing skills or chance, but something in between.
2. The hidden object games are absurd. The game tasks you to find stuff that have no relevant to the case but are just interesting. One can argue there are just as many other choices (in Sherock's flat, for example) that are equally interesting. There is no good reason why these other choices of objects are not picked.
3. The level-up system is largely irrelevant and feels tackled on. It exists only if you want to compete in the leaderboard (despite all of its problems).
4. Many of the clues make sense only if you are familiar with English vernacularism and geography. This is not necessarily bad, but it makes many of the puzzles unnecessarily difficult and cheap.
5. The "puzzles" vary from good to mundane. The gambling puzzle is clever. The puzzle to check off a list of names by their initials is just a chore without any cleverness at all. Even the word answers you choose in the Mind Palace feel somewhat arbitary in hindsight, as they are other words in the list that can be equally valid. I feel like a case where the designer sees only what he or she wants to see as the "valid" solution and conveniently ignores other arguments that can support other word choices.
BTW, the video frequently glitches. Often, it will not play on its own when it is supposed to do so. A workaround is to view the transcript which somehow triggers the playback (except in one scene in which there is no transcript button to press, and you just have to restart the app to see if the video will playback correctly).