This is one of the best toys I've ever seen. I don't care for most of the newfangled plastic, electronic toys...most of them are junk. This one, however, is well-designed and will entertain a baby as well as even a 5 or 6 year old, in my opinion. I used to teach music at the elementary school level, and I think my kindergarteners and first-graders would have loved it.
The controls are all easy enough to operate that even a 9-month-old (the suggested earliest age) can operate them easily...none of them require too much strength or dexterity, for instance.
It teaches real musical concepts (high vs low, fast vs slow, etc) and has an actual, properly-working piano keyboard. The keys work like a real piano's does; if I press down 2 or 3 or 4 keys, they will all sound together, and the sound quality is like an actual piano, not a buzzy toy. There are so many different modes (there are three main modes, but when you turn the music "page" it brings up different sub-modes) so there are many different ways to play with this toy. My kid has played with this for 2 months, and I'm still discovering new functions on it.
I like the piano so well that I am pretty vigilant about not letting my baby "pull up" on it...I want the toy still working when he's 3 or 4. :) If you are assembling this for a baby, I would recommend waiting to install the legs until your child is through with the "pulling-up" phase. Durability may be the only weakness of this toy; nothing has broken on mine, but I could see where if an aggressive toddler say, tipped it over and stepped on the music stand part, that might break off or something.
On the whole, though, I LOVE this toy! Music teacher approved!