I've heard it was better from CoM from multiple people who played it. Right now, my order is
1. KH1
Best storyline and fun, challenging gameplay, it's probably the only KH game that actually gives you a nostalgic feeling because the Disney ties in perfectly with the storyline. It actually had some relevance.
2. BbS
From what I've seen the storyline is deep and full of emotions, it definitely fulfilled most of my expectations in terms of the story. Still yet to experience the gameplay, but it looks fun a challenge
3. CoM
Emotional, flawless original storyline, but the Disney was really pointless. Good gameplay, but the random encounters killed the fun out of exploring.
4. KH2
Entertaining storyline in a poorly written way (does that make sense? Because I think it had more action). Good gameplay, but it's basically button mashing and it's too easy. KH2 had good ideas, they were just portrayed poorly.
5. Days
Slow-paced storyline with little to no influence on the series in general. Half of the game was about a bland, boring character that was just unnecessary (everything in Days could've been explained easily without Xion, you know it). The gameplay redeems it somewhat, I like the panel system. I also thought it was a bit repetitive. Get mission from Saïx, do mission, eat ice cream, repeat. It doesn't get good until around day 300.
6. Coded
Haven't played it, but the ending sucked :|