When it comes to Finn, I'd have to say I'm more disappointed than anything else.
I mean he's a stormtrooper, who's gone through all the stormtrooper conditioning, and on his first day on the job, he's so horrified by the terrors of war that his programming essentially breaks down. That's how I understood his origin. But not long after this, he's blasting people left and right (in the escape scene), which made both myself and my brother go "Holy shit" while watching it. It was just jarring. I know he's trying to escape, but if his attachment to life is so strong that his first taste of death fucking de-Terminatorizes him, I don't see how he can justify killing anyone, even, and maybe especially, his fellow stormtroopers. He more than anyone else should understand what they're going through. Now maybe I have something backwards here, but honestly, a Finn with a No-Kill policy seems to fit better with his origin, was where I thought the film was going with his character initially, and would have certainly made him more interesting than what's actually here.
Because besides that, he just seemed to fall into the typical black-sidekick character archetype. Keep the funny coming, make the hero look good type shit. Luckily John Boyega's so charming that I did end up liking him more than not. He just had so much potential.