There are a lot of people that look for and enjoy mechanics first, and narrative carrotsticking second (or third or fourth). Most of us are from the days of gaming where that's all there was.
I understand that many people love stories and narratives and characters first and foremost in video games, but some of us don't. To each his own. There's plenty out there for both sides.
That being said, MotN isn't anywhere near as good as Thief, but it plays better and I enjoy it more than any stealth game I've played since the Riddick games, and that goes for MGS as well. I wouldn't put MGS and MoTN in the same category anyway.