Yes, Mugen Souls offers both English and Japanese voice tracks. It is an option we’ve come to expect from NIS, yet the question seems to come up with an odd frequency anyway. I can’t speak for the Japanese track to any great extent, but the English track is excellent. Voicework is liberally sprinkled throughout the game – so there are some unvoiced story sequences – which is a bit of a distraction, but Mugen Souls makes up for the inconsistencies with personality. Chou-Chou is a "bad guy," but incredibly likeable, as is her supporting cast. There are a few one-note characters, but that’s just another of the genre’s particulars.
Visually, Mugen Souls is a lot of fun. It’s bright and incredibly "anime," but not to the point where its distracting. Chou-Chou flips personalities throughout the game, each offering a different look for the main character. You can even customize your peons, allowing a bit of self-expression. I should, however, mention Mugen Souls is loaded with suggestive visuals. All keep within the game’s "Teen" rating, but you will see scenes of girls bathing together and the like. Depending on your threshold, it might get a little uncomfortable, though I never got the feeling anything was included with the intent to offend.