Broforce have many types of campaign : World Campaign (with the world map and zone select), Arcade Campaign (no choice : all the levels) and Custom Campaign (you can download levels or make them
or buy them)
You drive a helicopter and select the zone you want to do. At the end of each level awaits a final Boss (Terrorkopter, General, Mammoth Kopter, Expendabros boss etc...) and you can't restart a level you have already finished, you have to restart the campaign. You can travel all around the world and kill seagull. The user generated island was also on this map.
Levels after levels and boss after boss, you complete all it's possible to play.
You can play custom campaigns made by the community on steam. Also, you can download levels (.bfc) and place it in the "Level" folder. Then you can go to "Custom Campaign", offline, and play it. You can already create your levels and, if you want, share it (you have to finish your levels before sharing them so don't create Mega-Hardcore-Levels).