I've probably missed the "in before" chance but; for the people who complain about Legolas being in the movies: He would have been there, everything we know about Legolas and his timeline points to him being in Mirkwood with his father, Thranduil, at the time of the events of the Hobbit.
Tolkien knew very well later in life that the original story he wrote (the Hobbit) no longer fit into his expanded universe, he made a lot of revisions and rewrote large sections over the years but what a lot of people don't realise is that at one point he began re-writing the entire book from scratch, you can read the 2 and a half unfinished chapters in the histories of middle-earth which are by themselves the same length as the entire first edition the Hobbit; JRR did eventually decide to let the Hobbit stand on it's own merit.
Tolkien did the Hobbit first and didn't really create or flesh out his universe until he was well into the LotR - Jackson on the other hand adapted LotR first, if Jackson stayed totally faithful to the Hobbit book it just would have been un-watchable as a complete set of movies, you could not call it a lord of the rings prequel.
I enjoyed the Hobbit movies a lot, there were some not-so-great bits and some so-so bits but overall I really enjoyed them. I think Jackson did a really good job considering the challenge that was in front of him.
To have the movies make sense and tie in with the pre-established cinematic universe he had to use information from books he did not have the rights to, he did this in an extremely clever way as to not make it obvious for the most part, for instance:
The white gems of lasgalen - The gems that Thranduil wanted from the mountain, some would say that this is a totally made up artifact and a totally made up story, people who are a little more familiar with the universe know that this whole storyline is an adaption of King Thingol's story and that the White gems of lasgalen are a silmaril.
Long story short King Thingol acquired a Silmaril (white gem/s), he then took them to the dwarves to be set in a necklace and they had agreed on a price for the service, when King Thingol returned to collect his Necklace the dwarves had been corrupted by the Silmaril (amplifying their greed) and they did not give it back to Thingol. Thingol then killed all the Dwarves who made the necklace (and many others) before being killed by the rest of the Dwarves in the fortress which ended up starting a war.
The story of King Thingol is widely regarded as what Tolkien later intended to be Thranduil's story in the Hobbit, or rather, the story of King Thingol would have been the story of King Thranduil but it would have meant re-writing the Hobbit which he had already decided not to do.
Jackson adapted this story and it is quite brilliant, the official story of the movie trilogy is the white gems were Elvish heirlooms that were sent to Erebor to be set in a necklace, Thranduil agreed to the hefty sum for the service but when Thranduil went to Erebor to retrieve the necklace and gems Thror had become too greedy, claimed the white gems for himself and refused to return them to Thranduil.
This is why Thranduil turned his back on the dwarves after Smaug attacked and gives Thranduil a real reason, a real purpose, for wanting to go to war with the Dwarves; it also explains why Dwarves and Elves dislike each other (which is never explained in either the hobbit or LotR books, the story of King Thingol which does explain this can only be read in unfinished tales).
Legolas' inclusion is smart from a movie maker's standpoint, it does fit in the lore, in fact it would be far stranger is Legolas wasn't there in some capacity, he was perhaps overplayed a bit as the super hero but the whole idea of these movies is to bring the Tolkien universe to a wide audience - the data Jackson had in front of him was:
A. Legolas is one of (if not the) most popular character from the movie universe.
B. According to the tolkien lore, Legolas was in Mirkwood at the time of the Hobbit.
It would take most people about 5 seconds to decide to make a call to Orlando Bloom at that point.
I didn't like the Tauriel/Kili love story, while I didn't mind Tauriel's character, the Elf/Dwarf love just isn't right by any amount of lore, extended or not, most decisions made by Jackson were pretty sound to the Tolkien universe but this one just wasn't.
Tauriel herself I thought was fine, there would have been a captain (several, actually), and there is no reason it couldn't have been a female Elf, and her character was very true to lore in that she was a Silvan elf (the traditional Elves of the woodland realm) while both Thranduil and Legolas were already established to be Sindarin elves - this is why Thranduil would not agree to a union between Legolas and Tauriel, in his eyes, she is a lowly Silvan elf.
There are many other things I could comment on (both good and bad) but I think this is plenty to give people who don't have the time to read the insane amount of lore out there a good reason why the Hobbit trilogy was not 100% faithful the book, and just how well Jackson did considering that all the lore he adapted he technically couldn't use (without changing/adapting them enough to satisfy Chris Tolkien's lawyers); He didn't have Gandalf name the 2 blue wizards because their names could only be found in extended works.