Ok, before you you wander into this fucked up little creation known as Koe de Oshigoto! The Animation, know that this is essentially and by all means of what I've heard is hentai, actually depicting sexual intercourse and the like.
Story: (3/10)
This is essentially hentai with story smothered all over it. Not equally smothered either, more smothered like a mother to an unwanted baby or something along those lines.
It's about some girl (didn't care to remember her name, seeing as it hardly matters) who, out of some distorted sense of duty, feels it necessary to assist her older sister in the voice acting for an eroge game. I really don't even think this was meant to "turn on" even the creepers who are into this kind of stuff, seeing as roughly 85% of the time it's just plain awkward. Not in the "you're too young to like it" sense of awkward, more the, "why the hell would she do that?! It'd be so much easier for her to just do it this way" sense of awkward.
Also, apparently she's underaged, and super sensitive to pornographic images(I mean, who better than the pornophobic amateur to do voice acting for an eroge? :D).
All in all, it succeeds in the sense that what it was trying to attain by groping around in the darkness is mediocrity.
Animation: (8/10)
Like the majority of 2010 anime, this is essentially the only decent thing about the show. I mean, why put vibrant colors and brilliant animation to a decent show, we'll just put it on this hell orgy of a sandwich known as Koe de Oshigoto! The Animation :D
Sound: (6/10)
I will admit, they did a damn good job voice acting the unnecessary and admittedly akward slurping and "pleasure" moans, although good singing in a shitty opera doesn't really matter in the end, eh?
As for the OP and ED tracks, to be frank, I don't even remember whether or not this show had 'em. I hope that explains enough.
Characters: (3/10)
These characters both completely lack morals and basic logic. The lack of morals stems from her older sister, who has no qualms about using her underaged little sister to voice act in an eroge, and the lack of logic comes from the little sister, who still thinks she owes something to the hollow shell of a person that is (apparently) her sister.
The support characters essentially stand back and critique the complete awkwardness that is this underaged girl's voice acting, which makes it (guess what? :D) even more awkward.
The only thing that keeps me from giving this section a 0/10 is that the younger sister is reluctant and maintains some sense of logic(which ironically conflicts with my original statement), but nontheless, they still all piss me off.
Overall: (3/10)
Overall? This show shouldn't be watched by anyone unless you're the kind of sick bastard who enjoys watching a 16 year old girl awkwardly stumble through a forced eroge voice acting career. Hell, even to those guys, it's still a hesitant recommendation.