Well, Might&Magic games and LoL are quite different ! I'll speak only about LoL 1, because that's the one I finished.
First, LoL's world is not as open as M&M one. Sure, each area is pretty vast, but you're generally in an area until the scenario wants you elsewhere.
That's not a critic; it's just to say that LoL is much more story-driven than M&M, which is more about free roaming.
Second, companions come and go in LoL, only your character stays until the end. In M&M it has always been about a group of adventurers, not just one.
Personnally, I love both M&M and LoL, but that's also a matter of taste.