Broken Base: At least one of the classes was completely broken in some way, according to the forums.
Then we had the "Heroes is World War II only silly" and "Heroes is not just World War Two". But there was something of a uniting factor: almost everyone agreed that it was impossible to be competitive without spending about twenty dollars on Battlefunds.
Crowning Moment of Awesome: The game's earnable achievements were 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 could turn invisible, had an ability to make themselves capable of dealing extra damage with their rifle, and had a Sniper Rifle. Suddenly hearing Clack-Clack coming from somewhere near you would prompt an Oh, Crap! response.
Ear Worm: The theme tune of the game was delightfully catchy. A loading screen tip even asked you if you could whistle the whole theme tune.
Gunners were easily the most-used class during the game's run. Their high health and Leg It ability combined with a rapid-healing ability and a short-range machine gun made them Lightning Bruisers that could overcome most threats thrown at them. A gunner with an RPG was all but a death sentence for anyone using a tank.
Long-range pistols for Soldiers and Commandos were powerful and made them deadly from a distance. They were especially useful for Soldiers, whose middling movement speed and lack of a speed-boosting ability made them all but the slowest class in the game.
During Thanksgiving of 2011, special "dragon cannon" RPGs fitting into the then-ongoing samurai theme were released. They quickly dominated games due to the absurd speed and splash damage of their bouncing projectiles. They were nerfed in short order.
Good Bad Bugs: The word filter in the game's chat could be bypassed by typing the word "slick" before whichever banned word the player wanted to use. The downside was the hilariously surreal and vaguely squicky element it added to players' profane rants.
The Scrappy: Commandos got all the flak, especially on the forums. There were loads of petitions and clubs aiming to cripple the Commando by getting rid of the very features that defined it as a Commando, such as Stealth and Sniper Rifle. Many servers allowed only a certain number of Commandos per team, and a few banned Commandos altogether.
The scoped SMGs and machine guns available for purchase were infamous for tricking novice players into buying them before quickly realizing they were exactly the same as the (incredibly weak) default weapons in all but aesthetics, save for the useless scopes.
The machete released for Commandos during the 2011 Halloween event. It was essentially a knife with a much slower swing speed and a marginally higher range. Infamously, players were tasked with scoring about 1,000 kills with the weapon within a number of weeks - a tedious and thankless feat at best that would put a dent in all but the most skilled player's kill/death ratio - to get the gold aesthetic upgrade. The developers buffed it in subsequent months, but it still remained unpopular, and players didn't bother much with the samurai sword weapon that was released a month later.
"Stop Having Fun" Guys: You were not to use a tank in this game. And if you saw someone using one, you had to keep on grilling them about it in the chat and not bother to use any weapons or explosives at your disposal to counter the tank.
Also, "camping", when a Commando hid invisibly in a small, concealed corner and picked off stragglers from afar with his sniper rifle. Beginning Commandos often used this tactic, but as they leveled up they found that more experienced players disapproved of it.