QUOTE (talkster5)
Online was the only thing I played.
Then you probably didn't notice the difference due to your inexperience in the original Halo. There were lots of strategies and quirks that worked really well in the original Halo. Due to the new array of weapons and dual-wielding, a lot of those won't work anymore. Vehicle usage is totally different due to them now being destructable, the homing capability of rockets, and the boost option. Turrets add an element to base defense and attacking. Certain areas of the environment are destructive, allowing you to reach rare powerups and weapons. There's also those explosive barrels, you can utilize to your advantage.
You basically have to learn to play the game all over again.