New store items, visual updates, and tweaks
Valve continues on with the updates to Dota 2, with the introduction of a full-fledged quest-based tutorial system.
As any former MOBA beginner will tell you, this is pretty much a must have for new players, and it's a highly appreciated way of growing the community. Guardians of Middle Earth did it, and it was a great way to acclimate people to the relatively overwhelming genre.
Beyond that, a number of tweaks were made, like new animations, updated sounds, new icons, the introduction of the quest system, and a ton of new cosmetic items. In short, it's a massive, massive update.
I'm enjoying Dota 2 right alongside of League of Legends. They're both very different experiences that happen to share the same genre -- give both of them a shot!