Heroes of the Storm isn't live yet, it's currently in a technical alpha and you can play with all heroes for free and some game modes aren't really locked down, but I like it. It's a strange twist on the LOMA genre made popular by DOTA and League of Legends, but it takes some stuff away, adds new ideas with a cast of characters many will recognize, each with their unique playstyles and a fun talent system to boot.
League of legends is an interesting twist on the LOMA genre, the base of the game is still as it was invented in the Warcraft 3 days with creep waves and towers and heroes and all that stuff that new players might find intimidating. League of Legends has no denying, you don't lose gold when you die and there are some elements of persistence here and there to hook you in some kind of meta-game much alike achievements do in other genres. It's a nice LOMA, but after playing it for a while, the community is still what makes it a little hard to get in.