The only multiplayer game I've played so far is World of Tanks, a team-based competitive game. You can play as a tank (light, medium, & heavy), self-propelled gun, or tank destroyer, from any of four countries in the era from WW1 to the opening years of the Cold War (currently USA, Russia, France, & German. There are also UK tanks w/ Soviet marks, and a Chinese Type 59. More countries to come soon.) Once you select your vehicle, with upgrades that you gain by playing, you get into an equalized random match on random terrain, and either destroy the opposing team or capture their flag. Because the teams are generally equal, victory depends solely on your skills and your teamwork. What you earn in experience and credits depends on your team's victory or defeat, and what you've done in detecting, damaging, and destroying your enemies. It's free to play, but you'll have to pay to get "premium" tanks, gear, and ammunition.
So far, the majority of my gear are American vehicles of Tier 3 & 4 (Tiers are level types, the more powerful the vehicle, the higher the Tier, from 1 to 10), with a Tier 3 Soviet M3 Stuart which was a prize I gained for completing the tutorial. Sometimes the matches get weird, as I end up taking a Tier 4 light tank to go against Tier 7 & 8 heavy vehicles.
I also heard that the company that made this game will also be making World of Warships and World of Planes.