Megaten is one of my favorite franchises. Played through all of the games from Nocturne->Devil Survivor 2, but haven't been able to finish any of the earlier ones, they all feel a bit dated and don't have the combat-depth, speed, or style I've come to expect of the series.
Now while I do love Megaten, I have to say after playing yearly entries (sometimes even two a year), the formula of "get basic agi/bubu spells and hit weakpoints" then "get mediarama" then "get party attacking magic" etc...is getting kind of old. Sure it's the BASE of megaten gameplay, but I'd say about 50% of any new megaten feels like a repeat of what I've already done a million times before "oh, ok, this guy blocks wind and fire and is weak to ice. Let's get the right demons to counter that" etc, etc...
Maybe this is heresy but I'd like to see the next major megaten, whether it's P5 or SMT4 or a new franchise shake things up in that department. I feel like Devil Survivor did a good job of that by adding in the map strategy elements and Raidou kind of mixed it up with the action. So I think it's time for more mixing up megaten to keep it fresh beyond just new story, new music, new style.
PS. Catherine was really cool