For me, the three newcomers that gave me the most hype were Greninja, Ryu, and Bayonetta
Greninja - I knew that generation 6 was going to be represented on the roster, but I didn't really know who it would be. When I first saw the shadow, I thought it was Mewtwo, but I wasn't screaming with excitement when Mewtwo was revealed. I was more like "Oh, no surprise" because I thought he was coming back after getting 2 mega evolutions and another movie, and I wasn't that interested in seeing him return.
Then the shadow was revealed to be Greninja, and I was shocked. Out of all the generation 6 Pokemon that would be reasonable picks, Greninja was the one that made the cut. Greninja was one of my favorite two favorite 6th generation Pokemon (and one of my top 5 favorite Pokemon as well) at the time of the reveal, so Greninja was the first newcomer that I got hyped to try out. When I got to try out Greninja, I really enjoyed his play style. In fact, he still remains my main to this day, and it's all thanks to Smash Bros that he is now my second favorite Pokemon of all time.
Ryu - When I first learned about the Ryu leak in April, I was really shocked that he made it in, especially since Sakurai made a previous statement about implementing characters from other fighting games would be challenging to do. Ryu in Smash was a childhood dream of mine that was crushed after Sakurai's initial statement.
Then came the Ryu leak after the Mewtwo update, and I was shocked and overwhelmingly happy at the same time; my childhood dream came true! I was eagerly counting down the days until he was properly revealed. When the second batch of leaks came along, I got even more excited to try out Ryu: his stage, his Smash model, and the new Ryu remix were all awesome. While the surprise would've been far better if Ryu was never leaked, just hearing the news for the first time that Ryu was on his way was hype-worthy for me!
Even to this day, I'm still really happy we have Ryu. He's fun to play as with his Street Fighter controls, and it really makes him stand out. He's also the fighting game character, coming from video game series that defined the fighter game genre (no doubt that is a major reason why we see Ryu being crossovered into so many fighting games). Smash Bros wouldn't have been conceived if Street Fighter never came into existence, so having Ryu in Smash is a great way to acknowledge that, and I really hope Ryu returns in future installments to come.
Bayonetta - The moment I saw Pit in the opening segment and him conversing with Palutena, I thought we were going to get another Kid Icarus character. Even when Bayonetta's voice first spoke, I still thought a Kid Icarus character was coming. Then Bayonetta was first shown, and I was pretty surprised. I was among the many who thought she'd be too mature for Smash. I was also 50-50 prior to her reveal; I never played any of the Bayonetta games, so I couldn't form a strong opinion whether or not I want her in Smash, but I did think she was a pretty cool character who could make for some really interesting moveset potential with her guns and spells.
Her reveal trailer came along, and I was blown away. She was implemented really well, and I think she has the most fun moveset out of all the fighters thus far thanks to her combos and bullet arts. Sakurai and his team also did a great job retaining Bayonetta's character while toning her down to fit the ESRB rating. To be honest, I really can't wait to give her a try when she is released; she's secondary material for me. She also gets points for having one of, if not the best Smash Bros reveal trailer out there (quite well done for the final character reveal).
Honorable Mentions:
Corrin - Admittedly, there is a part of me that still wishes we had Azura as the FE:Fates rep because she would be far more unique in terms of moveset potential; in fact, I wonder if we would have this much salt if Azura made it in instead of Corrin because Azura fights with a lance (she doesn't use a sword at all), dancing, and water-bending. Ah well, I really wanted to see some sort of FE:Fates representation in Smash 4, though I was becoming really doubtful with that due to Roy's inclusion and the fact Fates might be "too new". Well, looks like my thoughts were wrong and my wishes were fulfilled.
With Corrin's inclusion and the two Fates track, my wishes for Fates representation in Smash 4 were fulfilled. When I watched Corrin's reveal trailer for the first time, I actually did get pretty excited for him, mostly because he turned out far better as a fighter than I could ever imagine. In fact, I remember his dragon aspects in his moveset far more than his sword-use. He's another character that I really want to try out, not to mention another secondary material.
Shulk - I wasn't too interested in seeing Shulk at first, again largely due to the fact I wasn't too familiar with him, but when his reveal trailer came along, that all changed. I remember being excited to try him out because of his Monado Arts, and he became my 2nd newcomer that I was looking forward to trying out.
Megaman - Another childhood dream fulfilled, and he had an awesome reveal trailer to tag along with the hype.
Villager- June 11th, 2013 (E3 2013)
Shulk- August 29th, 2014 (August 2014 Direct) 
