I liked it. A lot. Granted the missions were boring for quite a bit but most of them were optional so I have only myself to blame. About my biggest beef with this is that the bosses had such ridiculously infinite amounts of HP. So unfair, wah @A@
As far as the plot goes, I've given up on the series' plot around the time of KH1, so the rather glaring absence of one sans Xion's existence didn't bother me. In fact, I'm looking forward to what they'll do with that one in the future seeing how she's mixing up Sora and Riku's Memories, and also keeps Ven in the mess.
Truth be told, I never expected all that much out of a game that told the tale of the Organization so I guess that also adds up with my lack of disappointment. Everyone and their mothers were expecting so much insight and depth for characters who only prove to be more filler with every installment they appear in, even with the trailers from the very beginning kind of said "sorry, sweet-things, you're getting a RAX game". KH is Sora's story and with Roxas not manning up for the task, they had to bring in someone who would. Pun partially intended.
A lot of grief people have with this game is how "OOC" everyone were. I personally didn't see much of a Character for most of those characters for them to be OUT of in Days. Roxas? We got him swinging between being an emo brat and a clingy, selfish brat. And lo and behold we got that in Days too. I can't even blame him for falling out of touch with Axel since Axel was, in fact, lying to him despite his best intentions, and Roxas was, well... what, half a year old at the time? Lacking Sora's Memories and having a fractured Heart that merged with his Somebody's, unlike Xion who had a whole Heart if Repliku's make-up is any indication, he couldn't really be all that much more so I'm somewhat forgiving in his case nowadays.
On the case of AkuRoku, I NEEDED Days. KH2 didn't convince me they were friends for any other reason than Axel clinging onto his Heart replacement. I didn't buy it, not in the least, with how Roxas treated him. So not only seeing how they got to be friends, but also what kept them around each other for a good while later, was necessary.
On the case of Namine, Diz, and Riku. I, for one, forever more will LOVE him in Days. I'm glad he stopped being the mission oriented prick who'd sacrifice the universe for Sora's sake, be it to accuse him of failing as a friend or to wake him up. The blindfold's meaning really added up to me in this aspect as well. And what can I say? With Namine being on the run from the Organization herself and needing to be by Sora's side, and Diz being the lazy managering prick that he is, if Riku couldn't bring himself to harming Xion, they were kind of stuck on that front. So I didn't mind all that much even the "stalling" of the plot.
So yeah. I've little complaints about the game in particular so much as the series overall. It's a KH game; at least it made up in character-orientation what the series lacks in plot.
tl;dr not being an Organization fan helped.