The only thing that could've helped Days was if Nomura had stuck with it being a game centered around The Organization and Roxas' time within it, that's what we were promised anyway, but instead we got a game about Xion and... No, no, that was it.
I'm not saying that it would've made the game instantly good, but it would've been better. The way the missions were structured was pretty poor, but it was doomed to fail even conceptually. It's meant to be a series of tasks you would expect the Org members to do, this pretty much means that you'd have to go back to the Castle after every mission, making it repetitive even before we get into the content of the missions. That said, the missions themselves were pretty uninspired, more varied objectives would have been nice. More varied locations would have great too, I know the DS has some serious limitations but come on.
The panel system itself I feel was fine, it could have been polished more but it was mostly fine. Of course it doesn't compare to the command deck because nothing does. I guess for one removing the spell casting limit would have been much better, that was pretty dumb honestly.
But yeah now I'm ranting, thanks Nintendo.