– Fili: The Viking-esque dwarf (and the elder of the two)
For reasons explained in the novel (and thus, major spoilers) I shall not expand much on these two characters. Suffice to say, 
they both have their particular moments in the story, added with a modest amount of characterization (though albeit, still weak).
Fili is the eldest of the brothers and thus, next in line to the throne after Thorin himself. Throughout the novel, Fili (along with his brother) retains the status of the most practical of the Company – often assisting in the hard-tasks throughout the Quest.
Unfortunately, we did not get much exposition in ‘An Unexpected Journey’, leaving viewers and readers alike to “fill the gaps” at particular moments in the film – mainly, the considerable lack of on-screen presence. Indeed, after my 13th or 14th viewing, I have yet to spot Fili in some of the Company’s major moments so far – the Trollshaws sequence, Rivendell, the escape from the Misty Mountains …
It’s not certain whether this is due to the fact that the original actor (Rob Kazinsky) had to leave during the first month of production (to be replaced by Dean O’Gorman). If that was the case, clues indicate 
that by that time, the film-makers had only tackled some scenes in Bag-End and Rivendell – giving quite enough time for O’Gorman to shoot much of the first film himself. Still, we rarely get a glimpse of him and the attention seems to fall rather on Kili.
Wielding two deadly dwarf swords, Fili’s character (along with his brother’s and that of Thorin) needs to move towards the spotlight, alongside Bilbo – in order to retain the essential qualities of the novel itself.
I actually feel sorry for O’Gorman since he seems to be the odd one out of all the dwarves. His lack of presence in the first film makes it difficult for viewers to bond with his character and I’m really hoping to see his performance in ‘The Desolation of Smaug’.
– Kili: The young trouble-maker (and the youngest of the brothers)
As soon as the first official image of Kili was released online, pretty much the entire fan community expressed serious concerns about the lack of a dwarvish beard given to this character.
Whilst fan girls drooled over the appearance of a (and I quote) “young Aragorn”, others were unsure about whether Aidan Turner’s Kili resembled more of a juvenile elf, than a dwarf.
Yes, Kili did receive some major concerns – all the more when, in the films, he was replaced with Ori as being the youngest dwarf in the Company.
Time has passed since July 2011 and whether fans have learnt to accept his appearance or not, Kili has made his spectacular entrance in the first instalment – performing acrobatic stunts and wielding a bow which makes him reputable for being a dwarvish version of Legolas …
As with Fili, in the novel he is portrayed as one of those who are ready to give a helping hand, and also are quick to favour Bilbo’s actions in the Company.
What I’m really anxious to see, in ‘The Desolation of Smaug’, is the exposition of the relationship between the brothers and their uncle (Thorin). Casual viewers have had no way of knowing the present ties with the Company’s leader and it is crucial that the writers “impose” upon their audience this very important fact.
Next post, the mighty Oakenshield himself …
A Tolkienist's Perspective 
I agree that Fili and Kili have some elf characteristics…and they probably look the way they do because they realize that Legolas had a cult following among women viewers. So I ask…why is Legolas in the next movie?
Some people say, “well he was old enough so it makes sense”. Well so was Gimli, where is he? And while we’re on the topic of characters who don’t belong. I don’t ever want to see Frodo again. I swear I watched Fellowship of the Ring the other day….Frodo fell down at least 5 times. He’s unbearable. no more flashbacks.
Yes, I think including Legolas was mainly for marketing reasons.
I would have loved for him to appear only as a short cameo – a non-speaking role, just being in the background during Thranduil’s interrogation of the dwarves.
Personally, that would have been more effective.
As to Gimli, who knows – we may yet see him 😉
I didn’t mind Frodo in the AUJ intro, but I agree that now he shouldn’t be re-introduced in any of the next two films and I think Elijah Wood confirmed that recently.
that is how i envisioned the Legolas character coming back, and I agree it would be more effective. I figured they would give me a couple of lines… but than I saw the trailer