Just Prism Red. The others showed up only in the classroom and during reverse pirating, I think.

I love Disgaea 3 <3

Classroom and clubs is really flexable and class-worlds offer an interesting way to power up character's attributes and shift skills around. I want them to keep that in some form.  KEEP!

Reverse Pirating = AWESOME :D KEEP!

Stat Stacking = Statistician stacking = win, keep! 

Magichange = Awesome. Except in Land of carnage when enemies use it and I'm unable to hit them anymore. it was an awesome idea.  KEEP!

Puppy claw stick. My god what a time saver, it was a bit over powered in patch 2.10 when you had a chance to cloning an item on every floor of Class-world but even with proper spawn rates, it saved me a good 40-50 hours of mindless grinding while not actually removing the need to grind. KEEP!

Sprites. I don't mind if Disgaea keeps the sprites vs 3d models, it gives the game personality. But like many have said they need to be upgraded (higher resolution), I realize for them its a huge pain as they've been reusing sprites from all of their games to save money and time (and we know ichi aren't precisely flowing in cash) but it would be worth. 

Online. More online integration would be just insane. how does Pirate/reverse pirate Duel worlds sound :D (where one player is on the pirate ship the other is on the field. 

Land of Carnage. I love land of carnage but there needs to be a final act in land of carnage, Super Land of carnage which absolutely retarded bosses that require perfect character builds to remotely stand a chance. Test those theory-crafting spreadsheet geeks :D

More Prinnies, More Prism rangers. 

More Prinnies, More Prism Rangers, MORE LAHARL (I want him as the main character again).

A better graphics!

Don't misunderstand me! I don' t want FFXIII graphics in a NIS game... I want it in 2D, but a PERFECT 2D (like Muramasa, Odin sphere, Blazblue...)

Yeah, I just want to see upgraded sprites. 3D characters would put me off.

Wouldn't say no to more Laharl either.

keep the visuals in 2d, but up the res of them

mabey online game modes

an Online arena would be a blast, since its a school and all.

Sharpen up the graphics, nothing HD as I dont want them to cut content for the sake of keeping cost down. Its always going to be an extremely niche title.

Thats it pretty much.

HD sprites, and Moar prism rangers.

They should include a world map a la Shining Force, a more serious story, HD sprite and online battle.