This game bangs!
It has:
excellent in-motion pixel art
excellent music
a very dark plot
most of the characters have very memorable looks and personality (Wylfred, Auguste, Fauxnel, Reinhilde, Lieselotte, Gwendal especially),
most of the in-game voices are superb
It is a strategic game with a very unique twist: dynamic reflex-based siege battles, where you have to time your characters attack by just pressing the matching button on the DS console.
Very easy to learn, but difficult to master the gameplay if you want to reach the safe threshold for 99% of the battles you'll fight (if you don't reach it, Miss Hell is going to give you massive disadvantages in later battles!)
It incentivises multiple playthroughs and experimentation and has a MASSIVE post-game.
If you can, give it a try!
Anytime the "Emergency Slash Line Stream" battle theme starts, it never gets old and pumps you up for the fray!