If you're used to the harmless evil of Disgea and come here expecting more of the same, you're going to be shocked, offended, or may even find the game unplayable. Metallica is genuinely despicable for much of the earlier parts of the game, so be forewarned. Personally, I enjoyed playing henchman for a protagonist whose evil was genuine rather than cartoonish, but your reaction may differ.
That out of the way, this is a truly excellent game. A mighty anchor title that'll keep you playing the previous gen console a while longer.
The combat is excellent. With a little practice you'll be agile, dangerous, and feeling satisfied. The screen is busy without being crowded, overhead warnings are useful without being patronising. Systems are heaped high without being convoluted. Just excellent all-round design.
Major characters who seem typical at first grow out of it quickly. The story is unusual- as it has to be, with a genuine not-for-laughs villain who doesn't suit many typical anime tropes. Sato Tenpei delivers a superb soundtrack to accompany the Hundred Knight, which comes as a surprise to nobody in light of the guy being a major talent. And finally, while I can't speak for the English dub because I switched straight away, the Japanese dub is up to the JP Voice Acting industry's usual standards of consistent excellence.
Do yourself a big favour if you're a NIS fan, a JRPG fan, and/or just a fan of mid-budget oddities that embarrass hundred-million dollar AAA's by matching their quality while far exceeding their courage and imagination. Buy this game.