You can literally read the entire book in the time it takes to watch just one of these three mostly pointless films. What was basically either a single paragraph or just a passing mention is now a full 15-20 minute scene.
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I mean, what the hell was that whole thing with the dwarves tricking Smaug into drowning himself in gold, only for him to shake it off seconds later? And Kili getting poisoned? And the chick from Lost? And basically everything Gandalf was doing?