Very very good. The only reason I don't give 5 stars is because of the strange difficulty curve : the first match are really hard (since your stats and your opponent's are close) but if you don't give up and try again your match until getting S rank (and finishing with a full S chart is one of the achievements), your power grows quicker than your opponent's and the matches become more and more easy.

To say it short, it was easier defeating Cthulhu (match 30) than a Thug (match 1) !

Also, it seems one of the achievements is bugged, "Holding back" : I won many matches without using arcane power AT ALL but it didn't check... ?