Broken Base: At least one of the classes is completely broken in some way, according to the forums.
Then we have the "Heroes is World War II only silly" and "Heroes is not just World War Two". But there is something of a uniting factor: almost everyone agrees that it's impossible to be competative without spending about twenty dollars on Battlefunds.
Crowning Moment of Awesome: The game's earnable achievements are known as "Heroic Moments", which is this trope. Heroic Moments include such things as destroying a flying plane with a tank or running someone over with a jeep.
Demonic Spider: Commandos can turn invisible, have an ability to make themselves capable of dealing extra damage with their rifle, and have a Sniper Rifle. Suddenly hearing Clack-Clack coming from somewhere near you will prompt an Oh Crap! response.
Ear Worm: The theme tune of the game is delightfully catchy. A loading screen tip even asks you if you can whistle the whole theme tune.
The Scrappy: Commandos get all the flak, especially on the forums. There are loads of petitions and clubs aiming to cripple the Commando by getting rid of the very features that define it as a Commando, such as Stealth and Sniper Rifle. Many servers allow only a certain number of Commandos per team, and a few ban Commandos altogether.
"Stop Having Fun" Guys: Never use a tank in this game. And if you see someone using one, keep on grilling them about it in the chat and don't bother to use any weapons or explosives at your disposal to counter the tank.
Also, "camping", when a Commando hides invisibly in a small, concealed corner and picks off stragglers from afar with his sniper rifle. Beginning Commandos often use this tactic, but as they level up they find that more experienced, hardcore players disapprove of it.