I have three children, ages between 7 and 2, and they all love this toy. They get most enjoyment when a friend arrives who's similar in size, because then they can balance the beam while pushing themselves around and around with the swivel action (and then suddenly stopping so that they nearly throw each other onto the ground -- oh, the games children play!).
The two-year-old can only play with an older child doing all the work, but she will stay on it for an hour if someone would indulge her for that long.
Gripe-wise, there's only really one: the spikes on the bottom of the seats don't half tear-up the grass! I suppose if the see-saw didn't also swivel, then you could put something like boards underneath the seats to protect the grass from the spikes, but the swiveling is half the fun.
In fact, my 4-year-old son -- who never does anything like it says on the tin -- enjoys ramming the spike on one end into the grass, sitting the toddler on that seat, and then pushing down the other seat until -- pop! -- out comes the spike with a sudden movement, and the toddler (squealing with delight, mind you) holds on for dear life as she's nearly catapulted into the brambles.
No ... really ... it's a fun toy, particularly for the price. All the neighbour kids envy it, and Dad likes it because it's so light and easy to maneuver as he prepares to mow what little grass is left behind.