Watch ProJared's review of Grimrock 2. I didn't get the impression the games were related, story-wise. And it sounds like they vastly improved with the sequel. Which is probably saying a lot, because the original Grimrock was really loved by old-school vets and fans of dungeon crawler puzzle games

Unfortunately I know nothing about most of the M&M series, so I can't help you there. But I've always been intrigued by the Grimrock games. So there's that at least. Sorry I don't have any firsthand experience though