We bought this for our daughter and frankly *I* play it every night. Me, a not-too-skinny, mother of 3 kiddos. I play this game until I am tripping over my own feet I'm so tired and the next day I can't wait to go back for more - never mind I can barely walk! It did take a few weeks before my joints got used to the pounding from the jumping and such - but a nicer mat with thick padding helps.
The song selection is varied and nice. The workout mode tracks your calories per song and per day if you choose. The training mode is very helpful for beginners for learning moves and the beat. Also nice for more advanced players for working out that spot you keep getting stuck in. I LOVE the endless mode (you have to play a lot of songs to unlock this) - you can create a list of songs to play and play them one after another with no breaks. SWEET!
In the game you have different levels of difficulty for each song - starting at the beginner level, to Light, Standard, then Heavy. Beginner, Light, and Standard are better compared to Easy, Medium, and Hard - Heavy is better labeled seizure activity. :)
Although we do own an Eye-toy, we have never used it with the game (we haven't got bored of dancing yet). The 2 games that can be played without the Eye Toy fascinate my children so they pass the mark.
One recommendation though - periodically save your game an a backup Memory card. I had unlocked everything and then the data was corrupted on the memory card and I had to start over from the beginning - not fun!
In summary, the folder of our Playstation 2 games is gathering dust - DDR STAYS in the playstation at all times and will continue to be used daily until we wear out the disk...