Here's what ya should do:
First of all, customize yourself. Color up and decorate your armor all you want; create your starting identity in the game.
Now, congratulations...you're officially within the world of Reach.
Then, go to Forge World and try out all the new weapons and stuff. Get used to the Armor Abilities, test-fly a Falcon, do anything and everything you can to get comfortable with the game.
Next, go to Firefight and go to Gruntapocalypse. That way, you can test out the new combat WITHOUT facing tougher enemies.
After finishing that, head to Campaign...personally, I want to have my first battle with a Reach Elite and Skirmishers and stuff in the story, not in Firefight...it makes the first encounter so much sweeter.
Play through Campaign on Heroic; if that gets tough: Normal.
DO NOT play on Easy or else you'll get bored real fast, and DO NOT play on Legendary first-playthrough or else it'll go from fun to "when will this torture end!??"
As for Multiplayer...heck yes. =D
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