Picked this up and just finished my first session, after 45 minutes I can barely walk up the stairs.
Told it I trained regularly and put my full force into the strength calibrations, and it's kicking my ass - not too much, but just enough that at the end of each level I'm pretty wiped. For those who were worried this is just for stay at home mums and soy boys, nope!
The ring device is surprisingly great. It can register everything minor to major compressions, and due to its form, it puts up more resistance the stronger you are, so it's a perfect one-size-fits-all exercise tool. I power lift 3 times a week and was squeezing that little bastard hard, and the game was just like "meh, you are doing okay I guess".
I'm sure could lower the settings and have it as a cake-walk, but the fact that it's picked a default just from the initial calibration that I find exhausting is impressive, and that's at about 20% off the hardest setting.
Gameplay-wise it's fun, or at least as fun as you can expect a game about exercise to be.
It's definitely more entertaining than just doing squats to music, and having the game track your progress with its little RPG elements is a real added incentive to exercise, it also forces you to mix things up and therefore I think It's probably giving me a better work-out than I would give myself. As the game opens it I'm sure it'll teach me some new moves too, and whilst it can't correct my form etc, it does a good enough job of making sure I'm not completely bodging the moves, and the tutorials are easy to follow.
There is clearly some clever psychology behind almost everything in the game, even subtle things like when you hold a move you see the body part it exercises as the 'weapon', and the more effective you perform the move, the more buff that weapon becomes. So stomach exercises, your weapon is a big fat beer belly that turns into rock-solid abs the longer you can charge it before attacking. It's constantly throwing positive reinforcement at you, EXP, gold, showing me how many calories I burnt, levelling up.
The only disclaimer I would add is that this isn't a game with exercise elements, this is Nintendo making an exercise title. If you don't want to sweat, it's not for you. You are not going to come back to this just for the gameplay, you'll come back to this as you want to do exercise and enjoy what this adds on top of that.
Wardrobe warning - The leg strap keeps slipping down on me which is annoying, you can't really wear it on bare skin nor put it over baggy gym shorts, so I'll need to get some cycle shorts or something.