MirrorMoon is probably not a game for everyone, but it provides something that few games do. I had about the same feeling with this game as I did with the later stages of Fez (which might be familiar to more pepole), when the game becomes more meta-gamey and disorienting. In MirrorMoon, you as the player never really know what to do (or even how to do it) but it's this 'enigmatic' quality that in the end kept me looking for the eventual solution (solution for what?).
So, even though the game might be obscure, frustrating and boring at times, it at least never ceases to be beautiful. Most importantly, special discoveries you make have a unique quality to them and the sometimes tedious parts before really let you know that it was you - and only you - that found out about this.
For a lengthy interview on design decisions, this is recommended: http://www.rockpapershotgun.com/2013/10/16/the-blind-night-discovering-mirrormoon-ep/