I saw this listed on a website for MM games, and had never heard of it? Has anyone played it? Is it any good? What is it like? Does it play like the early [MM1-6] or the later games?

Dark Messiah is a spin-off with combat-centric gameplay and is quite different from any of the main games. It features some standard RPG elements (skills, spells, inventory, etc.) but has linear level progression instead of an open world. You also control a single character rather than a party. I enjoyed it a lot, especially the combat.

There is a demo version available so you could try it yourself. :)

So in other words, it is like Crusader of Might and Magic. 1 player running as wizard, thief or knight? Since it it linear, does it have alot of quests that have to be done one after the other, or is it a hack and slash/level up for harder monsters?

Dark Messiah was a very enjoyable game. Though very different from the M&M or HoMM games, it does not shame the Might&Magic name. It is more like the later M&M games since it's real time, but it differs in that it's single character and thus more like Thief or the TES games, but more linear and with better combat. The best thing about it was that you could use the environment against your enemies, which is all too rarely seen in games.

Also of note: Dark Messiah was made by Arkane Studios, the same developer that created Arx Fatalis (and more recently, Dishonored). If you enjoyed Arx Fatalis, you'll probably enjoy Dark Messiah. If you haven't played Arx Fatalis, you really should get it here on GOG.

It's a first person action game with some light RPG elements. I wouldn't necessarily say it's sterling quality, but it's competent and goofy enough that you'll probably find some entertainment between the laughably bad plot and murdering everything with the kick.