I can't put my finger on why - but I agree with you.
There is nothing startlingly original in any of the elements of gameplay but what it does, it does sooooo well.
If WoW is the ultimate dungeon crawl MMO, this game beats it. Even the levelling dungeons I have played, which apparently are basic compared to what comes at end game, have a variety of different boss battle dynamics which is easily as good as WoW (albeit they are a little easy).
If GW2 was the ultimate game for open world battles, this game beats it. FATES are fun varied many and have a plot which ties into the plot of the local area of the game making it feel part of the experience rather than a tag-on levelling option disconnected from the min game.
If SWTOR was the ultimate game for storylines, well........it isn't anymore, whilst the voice acting is pretty poor in ARR, the storylines are engaging relevant and have a sense of place with the rest of the Final Fantasy series which means for a fan - they are awesome.
All we need to do now to really make this fly is create a fantastic community ingame. If we have that then this will be just about the perfect MMO. Sure so certain elements may be better in other games, but in terms of overall delivery there is no other MMO that packages it all up so perfectly.
Good job Yoshida san.