Armor Lock isn't overpowered. You just suck at Reach :)
Reach isn't bad, you're just a BK :)
For my gamertag, look up "Ghoulishtie"
ODST only has a new campain, and a new co-op mode.
However, it does come with a 2nd disc that contains all the current multiplayer maps, and it also has the 3 new (2nd)mythic maps.
And before you ask, no, nothing from multiplayer will be how ODST's campain and co-op is.