From Steam's DLC pages for Fall of Cybertron:
Download the Multiplayer Havoc Pack to get 5 new characters (WHEELJACK, ULTRA MAGNUS, BLAST OFF, PERCEPTOR and ZETA PRIME) for use in Multiplayer.
Dinobot Destructor Pack:
Download this pack to get 4 new characters (SWOOP, GRIMLOCK, SLUG and SNARL) and their associated parts for use in Multiplayer.
Massive Fury Pack:
Download this pack to get a host of new characters for Multiplayer (AUTOBOT HOUND, KICKBACK, SHARPSHOT and HARDSHELL). In addition you also get the Generation 2 BRUTICUS colors and 2 unique weapons for use in the single player Campaign (Retro Blaster and Shock Cannon). Lastly, G1 OPTIMUS PRIME is also included for use in both the single player Campaign or Multiplayer.
Based off of that information, it sounds like each one has extra multiplayer characters, and only the Massive Fury Pack includes some skins. The Massive Fury Pack also includes some new weapons for use in the campaign.
It doesn't look like there's any extra content, other than the characters. No new maps or game mechanics at all.