[quote name='donbaloo']DLC for Gears 3 was mostly multiplayer maps and skins right? From what I can tell, there was only one that added any campaign gameplay. Was debating waiting for GOTY but I never play online so it probably wouldn't be worth it for me if the above is true.
That's several recent deals on the game, maybe Gamefly'll let it fly for 10-12$ soon?[/QUOTE]
RAAM's Shadow is the only campaign add-on. It is actually a very good add-on tho! (It introduces old mechanics that have for some reason seemed to have died off in the latter Gears games.) Downside there is some contradiction between the campaign and the dlc, as you will come across. Also there are achievements which you will need to play online to get. (Like the Killing Cogs as a Mauler by reflecting bullets, which only the 3rd and 4th player are.)
All of the other DLC's add to the Multiplayer aspect. If you become a hard core Gears fanatic then there is Fenix Rising which let's you re-up (prestige) twice. (reminder, level cap is 100 before you can re-up). Each pack comes with some sort of multiplayer skin as well.
tl;dr Buy RAAM's Shadow at least.