First things first: if you don't know the game, I'd suggest you skip this. Honestly, chances are, you'll find it boring and/or simply incomprehensible.
BUT. If you play, know and love the game (the three things are interconnected: you can't play it if you don't know it, and you can't but love it if you know and play it), then you'll be able to understand all its intricacies. And you're just gonna love this drama! ^______^
The script is close to being perfect: the authors' love for mahjong transpires from every scene, the characters are written tridimensionally (quite a feat, given how they're stitting at a mahjong table the whole time!), and the "villains" are not so villainy after all, but rather opponents who could end up being friends under different circumstances (Harada is imho the kind of "villain" - again, quotation marks - that every writer would love to create!).
Although they also play several episodes by "house rules", those are still totally realistic or at least plausible, The moves, the strategies, the discards...all of them are realistically depicted, and as a player myself I'd almost always play exactly as the characters do, discarding the same tiles etc. - sign that it's well done (true, their discard-reading skills are sometimes a bit more than normal, but it's ok, seriously).
The cast did a marvelous job as a whole; just as in "Akagi" script and cast had gone hand in hand (unfortunately, in that case, being both lousy!), the same happened here, but in this case it meant that a great script was performed very well; kudos to all of them.
Some nice music, direction, editing and photography complete the package.
Perfect 10, as far as I'm concerned.