OreImo has had something of a controversial history. And that's not too much of a surprise-- it pushes the notion that wanting to bone your (perhaps nonexistent) sister is perfectly fine. Mind you, there is nothing inherently wrong with incestuous themes when handled maturely. But OreImo is not mature. It had no intentions of being so.
And yet, there was still more to OreImo than the incest appeal. The first season provided a social commentary on otaku culture and its perception in everyday society. It focused on characters that behave and react like human beings do, sometimes even at the cost of likability. When Kyousuke expressed any interest in his sister around others, he was treated like a pervert and smacked upside the head. It almost wanted you to feel that there was something wrong with Kyousuke's and Kirino's growing relationship. Not entirely, perhaps, but there were always deeper, more intelligent themes than "hey, this dude likes his sister".
OreImo's second season has none of this. There is no social commentary. There are no believable characters. Whatever the series had to set itself apart from any other ecchi or harem series is now gone.
The characters are relentlessly crippled by this downfall and Ayase receives the full extent of it. She was characterized as being level-headed and diligent in the first season; the proverbial "model student", albeit with a tendency to berate anybody she sees as odd. Where is this in the second season? Apparently nowhere. Ayase has become victim to the 'yandere' stereotype, cranked up to eleven, knife and crazy-eyes included. For no conceivable reason, she also develops (and acts on her) feelings for Kyousuke, entirely contradicting her belief that Kirino's happiness is most important. The most believable character in the series has been reduced to wrapping paper.
Kirino is a love-or-hate character, and whichever side you lean towards, the second season is not going to do much to change your mind. There is plenty more of the rampant complaining that she was so known for in the first season, including an episode comprising of her lying to Kyousuke, insulting him and proceeding to slap him across the face. I could never really get myself to hate her, though, because while she embodies everything wrong with teenage girls, there are always signs that she has remorse for her actions. That and the fact that she's voiced by Ayana Taketatsu.
You will likely develop a more positive opinion of Kuroneko, though. For the middle third of the story, she is made the principal character. A love interest, too. And unlike the rest of the female cast (Kirino excluded) whose feelings seem entirely forced and superficial, Kuroneko's feelings for Kyousuke are explored in detail. Her love is genuine. It doesn't feel shoehorned in to add an extra number to the harem, and that is perhaps the greatest compliment an anime like this can receive.
But her story arc eventually blunders about. It is marred, like most things, by superfluous drama at the end. The end of Kuroneko's arc simply consists of Kirino screaming at Kuroneko for the entire episode. Worse, Kuroneko's motivations are not even established once the conflict is finally resolved. All we get are a few ambiguous statements which further contradict her actions. What an awful note to end it on.
That's not to say that everything has gone wrong; a few of the episodes are legitimately good. Kuroneko's lighthearted episodes exemplify the good points of the series (and are wholly adorable), while Saori's backstory provides an interesting glimpse into the life of otaku while fleshing out her character in equal measure. The show is plenty capable of being fun; it just regularly chooses not to be.
The ending will leave many scratching their heads. It might even be misleading to call it an ending, as it wraps up nothing and shamelessly expects the audience to follow up with the OVAs for answers. Still, it's a nice way to detail Kyousuke's and Kirino's relationship as children and shed some light as to why they act the way they do. Suddenly Kirino doesn't seem half as infuriating as she used to.
Technicals considering, OreImo 2 is an impressive anime. It looks better than the previous season which was already impressive in itself. There are few scenes where the artwork manages to dip in quality, and the depth of field effect between character and scenery achieves in giving the show a more professional look. The facial expressions are also drawn and animated fluidly, which serves well to enhance the comedic scenes and portray the emotions of each character.
The sound is nothing spectacular but does the job perfectly fine. Occasionally the soundtrack works to the story's advantage, and scenes that would otherwise feel hackneyed are instead able to stir up a few emotions. On the other hand, the opening is a generic J-Pop song that you will forget almost immediately as it ends. The ending sequences are pleasant, though perhaps not as much for the animation or songs as they are for the variety. It's hard to argue against a new ending for every episode.
OreImo 2 is not a bad anime, but it is a bad sequel. Whatever you found appealing about the first season is likely to be gone here. It is made to be palatable solely to harem fans and incest fetishists, and those stuck somewhere in between are bound to find this season lacking any sort of cohesion.
A good sequel aims to improve, not to throw away everything that made it unique in the first place. OreImo 2 is a fundamentally broken anime.