The three DS hard modes are amusing. Dawn of Sorrow isn't THAT much more difficult. Portrait of Ruin is significantly tougher than the main game (Enemy damage goes way up! 100+ from medusa heads!), and it's kind of like a minor warning about Order of Ecclesia, which just wrecks you. Sorta.
I, um, finally did Hard Mode Level 1, only to find that it wasn't as bad as I thought. of course, I wasn't starting fresh, so with all the HP/MP/HEart upgrades and gear, I was pretty much Level 30-something in ability. But NOW I have 255 mode up, so I can increase each attribute one by one while levelling!