Battlefield Heroes is a third-person cartoon style shooter MMO game.
The two sides, the Royals and the Nationals, are cartoon caricatures of the British and German forces in World War 2. The sides are equivalent in their classes, abilities and, apart from the requisite visual distinctions, their vehicles. Since neither side has access to any toys that the other side doesn't also have, there's very little to worry about in terms of game imbalance, at least in terms of the overall battle. The distinctions between the classes is another matter entirely.
On top of the overall class system, there's the opportunity for players to spend hero points and valor points to upgrade their abilities and purchase new weapons and boosts. Experience points are earned through regular play so they'll accumulate over time even if you're not a power player. Earn enough and you'll level up and gain the option to increase one of your class's core abilities.
The nice thing about the system is that you can refund your points at any time and try out different specialties. If, for instance, you find that the Gunner's keg bomb is lame you can happily trade in those points to try out the frenzy fire power.
The real verdict is that Battlefield Heroes is a lively and dynamic version of the series stripped down to the undeniably appealing essentials. By eliminating all the complexity and distraction that has invaded the Battlefield series over the last seven years, the designers here have proven just how solid the fundamentals are -- two teams, a few vehicles and a couple of flags. What more could you ask for.