I liked The Desolation of Smaug as well, much better than the first one. That was spread far too thinly, this film is a more condensed ~150 minutes of action and storytelling. Add in better characters, and it is getting more towards the LOTR product.
As a Tolkien fan I also have no problem with Jackson creating a key character. The Tolkien universe is not supposed to be restricted. I've also always thought Evangeline Lilly had an elvish appearance, so had to smile when she was cast. She's actually one of the better characters.
I thought Jackson went a bit too far over the top with Legolas' fight scenes.