The best games often are the quirky ones with long, challenging learning curves. I'm just about ready to declare ARMA3 the best computer game ever made, or at least, second only to the phenomenal Eve Online.
Released over 5 years ago, unpolished and without much content - a partial campaign and just a half a handful of vehicles - the game has slowly established itself as one of the most successful titles on Steam. Until recently content has been added gradually by the developer in the form of DLCs and expansions. More is expected from 3rd parties - BI have already partnered with other studios and even the Red Cross (no other company was interested in their offer). The richness of features and interplay of different components is staggering, from the detail of infantry movement and guns benefiting from bipods when prone shooting to vehicles having thermal vision with different modes and missiles implementing different flight types; armored and airborne transport is copious and helicopters can sling load supplies or heavy equipment. The maps are so large that even jets fit in unlike in the Battlefield series. Latest addition are anti-radiation missiles (SEAD!!!
The design is centered on high moddability - and the community has been busy! Steam Workshop is loaded with various missions, game modes, units, mechanisms and utilities, some very serious and high grade. The just recently published WarMachine game mode feels like a nice fresh take on the classical combined arms shooter themes, with an infantry focus but you can also use various vehicles and call in support like artillery, air strikes, heli transport and supplies. On the other hand there are modes going back 15 years to Operation Flashpoint and with a full scale war/economy like BECTI where you build your own private army and fight over the whole island - the game can take around the clock or more. RPG servers are more like a traditional MMO experience. And there is a deathmatch mode where you die in a few seconds after spawning - can't understand why somebody wants to play that but they do, the ARMA community is rather large nowadays.
I think there's currently some misconceptions about ARMA - the franchise has evolved, moved to the mainstream (or the mainstream moved this way?), and is now giving the cookie cutter shooters a run for their money. True there's a learning curve, and just knowing where to start is an issue. But the game does a fairly good job of easing you into it, there's tutorials and of course the various showcases and a storylined campaign. In multiplayer, the zeus mode is a unique yet accessible experience and for a traditional shooter like experience there is KotH and others. Learning to use the editor or zeus provides you with a very powerful learning platform.
It's like I've adopted 4-5 different games when playing ARMA 3. It grows gradually on you - you can take a break and come back later and fall in love again when you find something that's just suited for you. Again it has been proven that if you start from a very different proposal than the competition you can build a very unique experience.