2014 was the best for me. The Smash stuff was hype, the new Zelda looked amazing (and I for one totally believed it actually was coming in 2015), Splatoon was a great announcement, and it was the first time they did the whole Direct/Treehouse/Tournaments thing and they nailed it.
This. We haven't seen any big new IP like Splatoon since then (ARMS is not such a big thing). I really enjoyed the Direct/Treehouse/Tournaments and I'm really happy that they continued this concept.