MOBA (multiplayer online battle arena) is a game where small (usually 3-5) teams of players fight each-other on a relatively small map. Each player controls one character who gains levels and equipment through the game. In most, players start from opposite sides of the map and work your way through pre-set defenses toward their opponents' base. As to why it's fun, that's harder to say, but there is a competitive aspect and a cooperative aspect as well as tactical and strategic decisions and a little bit of RPG thrown in for flavor. If you are interested, most are free to play. The big ones are League of Legends and DoTA2, although there is also Heroes of Neworth, the Stardock-published Demigod, and many more. if you are looking for a more casual version and are a fan of Adventure Time, Adventure Time Battle Party on the Cartoon Network webpage is pretty fun.

EDIT: Also this genre started as a mod for a traditional RTS, so camera angles and controls are very RTS-ey.

A tad unrelated, but here's another RTS from Stardock: Ashes of the Singularity. It will focuses on large scale battles and will use the Nitrous engine. 

There was this old game where you played RTS but the spin was that you built mechs as well, and you collected parts in battle from blown-up mechs. Anyone remember the name? It was divided into underground, ground and air maps. 

Do you mean "Metal Fatique" Heavenfall?

That's it!

*SIGH*     Seems like the casuals will like it based on my experience....

I'm starting to think that it will be a loong time before something like Dawn of War: Dark Crusade or Company of Heroes will be released again....

I wish Sins 2 would announce with a founder pack so I can get in line