The development cycle for this game is unusually long however, which makes me wonder why. 

Seem obvious to me; it's their first HD-level project, and it's a massive open world game. Logically, it would be a very time consuming undertaking.

Not really a wise business move, maybe I overestimate Nintendo. :D

Hey, I never played Xenoblade Chronicles, or all that many typical jrpgs, so I don't know what makes that game special. I prefer nice looking compact worlds where there's lot's to do though. 

I wouldn't mind to see Monolith Soft work on some classic Nintendo ips after this, but some "hardcore" Nintendo fans probably won't like that lol. Paper Mario could suit them. 

XB's hook is basically enormous open worlds, which are already difficult to build in the level of quality XBC X showcases, and as we've seen with countless studios including Nintendo EAD, first time HD development is a tough transition, which is probably why they went with conservative titles for their early efforts, like Nerw Super Mario Bros U and Nintendoland. Monolith jumping straight to an open world epic is like running before you learn to walk, hence the long development time.

Calling him a compitant musician is also an opinion. What of it? Whether it's used compitantly or not is an opinion coming from an area of serious expertise on the subject. Saying that Other M has a poorly written story is also an opinion, but coming from someone educated in writing, it holds more weight. I have that education in music. You're not going to see a composer like that making such sloppy application of his music. You don't just write two minutes of build up like that for no reason. When it's applied in real time and in full, the way it was intended when he wrote it, it will be used the same way his other songs of the same ilk were used, because that's why they're written that way in the first place.

I think Super Mario 3D World, Mario Kart 8 and DK: TF were all better than their predecessors. So not sure if I see this "struggle".

Unless you're talking about delays, but Nintendo isn't nicknamed Delaytendo for no reason... And Zelda U also looks more ambitious than Skyward Sword and will have a shorter development time.

And yes, SMD3DW is more ambitious than SMG2 (which was very similar to SMG).

They obviously did cut some corners to shorten the development time (i.e. sucky and lazy battle mode in MK8 and the isometric perspective in SM3DW), but the games were still great overall.