Aki's route is on my list of 'top five little sister routes of all time' for good reason. Aki's and Hidetaka's relationship throughout the VN, save in her path, is absolutely horrible. There is no other single path in this VN that reveals more about Hidetaka than this route, as it rips open the wounds that severed their relationship in the first place. From here on, it is all SPOILERS, so I don't recommend that anyone who hasn't read this path continue from here on.
Since Aki is a heroine, it isn't really a spoiler to say that she is a total yandere once she does go love-love on the protagonist. I love yandere heroines (so many fun antics) and Aki falls in with the best of the non-violent ones. There are echoes of Kaede from Shuffle in her (the anime version, not the VN version, lol), though the degree to which Aki's hate turns to love is a lot more intense than with Kaede. This is further enhanced by her personal circumstances (her illness).
Edit: For those who are interested, Aika's route, which was included as an addition to the original game, is fairly good for a sub-route, though it lacks the impact of the latter three routes of the game (Aki, Kizuna, Accela) In terms of quality, it is about equivalent to Rin's or Nozomi's routes. There is one thing I'd like to mention, having completed this entirely... Reminiscence reminds me of how frustrating Kinugasa Shougo can be. This guy absolutely hates actually completing his stories, so reading VNs by him always leaves you feeling like you are waiting for a sequel.