Different classes, gadgets, and uncapped level progression.
EA and Dice continue to try to walk a odd tightrope with 'Battlefield Hardline.' It's a game that is clearly 'Battlefield' in name, gameplay, engine, etc., and yet, it's positioned as somehow distinct from the 'Battlefield' series. Not only that, but the game has had serious dev time since the public beta last June, and thus, expectations are that the game has grown in its identity.
For those who want to see just how it's all shaping up, you are in luck. There will be a public beta on all five game platforms. This beta, which does not yet have a date, will see the debut of Hotwire, an all-new game mode. The devs are hoping that players will put a lot of time into the beta and have not put any kind of level cap in place. The Conquest mode will support 64 players, and apparently all of the current classes will be available as well as different gadgets.