Fun, stylized, arcade type boxing game. But you won't want to touch it after the first time.
The controls are a bit tricky on Swing Mode 1 but Swing Mode 2 is great. Feels pretty natural. I didn't try the other control schemes because I was looking to have a more natural experience. The American voice acting is actually pretty suitable, not too bad, though it isn't on the caliber of the Japanese voice acting. Some characters are pretty well done such as Kamogawa Gengi (the Coach) and Makunouchi Ippo. But others like Takamura Mamoru aren't that great.
Graphics: Great, but the manga and anime art is far superior. There's a bit too much shading and the lines are a bit too thick. Still good though. Also, your boxer should have been more transparent, it gets hard to see the opponent's punches and openings sometimes.
Right, so main point is about the "workout." I practice Martial Arts and Boxing regularly so I was hoping this would be a fun way to burn off some extra calories. Unfortunately, in my 2.5 hours of playing, I barely broke a sweat. That's despite the fact that I don't have good stamina. Pretty disappointing, but at least it's better than playing something while lying on the couch. I wanted to point out this part for other people who were expecting what I was.
Comparison with Wii Sports' Boxing:
It's important to understand that this game is played more like an Arcade game, rather than a Simulation game. So some things here are almost "unfair." Some characters are overpowered, such as Ricardo Martinez and Takamura. But that's because this game is based on an anime / manga series. For the same reason there are some stylized techniques such as slow down technique which makes the opponent look like they're moving in slow motion. It's all done on purpose.
Wii Boxing on the other hand is a different type of game. The punches aren't as sharp or precise and there is no footwork involved. However, in Wii Boxing the swaying, and leaning (to dodge) are excellent. And the blocking is done with your hands. In fact, you can pretty much do whatever you want with your hands (make poses, etc.) once you get used to the controls. Except punch properly. And if you want to sweat, Wii Boxing is what you're looking for.
Of course, neither game is a substitute for actually practicing in real life. Approach the game as just that, a game, and don't set your expectations too high. VBR is an okay game, and it's only for the hardcore fans of the manga / anime series. I played it once through, and never again.