What should I know before playing Dark Messiah of M&Ms?

* Get the Unlimited Edition mod - it really improves the game (New Game+ is great):
http://steamcommunity.com/sharedfiles/filedetails/?id=739039320

* Don't play on Hard - it buffs enemy health and damage without making the game the least bit more interesting.

* The simplest thing you can do to dispatch an enemy on the rare occasion when you can't kick them directly off a cliff, into some spikes, into a fire, into a spikey fire that leads off a cliff... throw / kick a physics object at them or kick them off something to make them fall down and go into ragdoll mode. Now do a power strike with a bladed weapon to impale them. Impale is (mostly) a one hit kill, and the reason why bladed weapons are superior to everything else.

Edit - a number of commenters claim that blunt weapons can also impale. I'll have to check when I next re-install the game.

* If you got to an enemy a bit too late for the impale animation, just kick them again. It's a lot easier to keep a prone enemy ragdolling than to ragdoll a standing enemy.

* Once ragdolled, enemies can be kicked wherever you want them to go, or even picked up with telekinesis and thrown around.

* Drop a shield into your hotbar. That's the only way to get the game to remember you were using a shield when you switch away from and back to your melee weapon.

* Most magic spells are fairly boring, doing straight up damage without taking advantage of the physics engine. The only ones that are really recommended are the healing spell (a very minor investment for a huge return, so HEAVILY recommended), the freeze spell (enemies slipping off cliffs and stairs will never not be funny) telekinesis (handy for grabbing secrets) and charm (great for clearing rooms filled with enemies).

* Stealth is kinda bad, until you get stealth 3. At which point enemies will only notice you if you jump around under a bright light.

* In general, a good first playthrough build is a basic warrior with minor magic investment. Stamina, Melee 1-2, Telekinesis, Heal, Alertness, Endurance, Archery, Strength. Not written in stone, but a handy guide. (You can experiment when you hit New Game+ or when you have an overt abundance of skill points)

* Conversely, don't pick Burglary. None of the really good secrets are behind locked doors / chests, much less doors / chests that require Burglary to open.

* The game has a lot of secrets. Explore out of the way spots as often as possible, and you'll generally be rewarded with some neat items. On that note:

* Once you get the rope bow, use it constantly. If there's vertical space with a wooden surface above you, there's a fair chance it's hiding a secret accessible with the rope.

Let me know if I this guide helped you - or conversely, if I missed anything terribly important.