Onion Warfare One
Onion Warfare One can be played solo, or with a few buddies.
It has boats, it has rocket launchers, it has FUN!
It has a version with no voice acting.
Extract the .pbo file(s) to your ArmA3\MPMissions folder.
I'm not new to Arma mission making, but I'm no expert either. I usually focus on small missions with a fireteam or a squad and 1,2 or 3 objectives that can be completed without dying (too much) in a relatively short amount of time.
I also like to sprinkle a little bit of humour in the briefing to remind us that it's still videogames after all, you don't always have to be in full milsim serious mode. Hence my most famous (in very restricted circles) mission in Arma 2 entitled Chicken Hunt, where you had to assassinate a chicken to stop terrorists from taking over the world using the H5N1 avian flu virus.