My older son (who is 7) also plays with lego in it so our 2 year old can't get the small pieces! Heaps of uses!
ours is now being used for the same purpose quite often as Oscar has discovered the joys of "real" not Duplo lego!
We bought ours second-hand when Ozzie was 5 mths. Its wooden, large and hexagonal, on wheels and he got SOOOO much use out of it. He is an independent player since very early, perhaps thanks to it too....he'd be in it for dangerous cooking time, for while we washed the floors and didn't want him running everywhere etc. He scaled its bars at 1 yr 8mths and we then took off three bars (they come with springs adjusted for this and it then became him playden where he could come and go as he pleased.
With Emma, we weren't as good at getting her used to it and didn't have as much timr to allow her to play completely ALONE as Ozzie is always there, or at least almost always there. But I do use it for her if she has an EW and I am getting ready for work in a hurry and DH is still asleep....Emma can also scale the bars already but given enough interesting toys and provided her brother is in it with her or somewhere close, she will play happily for up to 20 or 30 mins inside....
Ours is on its last legs though, as two weeks ago we had friends over with 9,6 yr olds and 5 and 2 yr olds. the 9 yr old decided she would use the playpen as a "waltzer" type amusement ride for the other kids and with them all in it together it lost a support piece on the bottom. when I am away in the summer DH is going to dismantle it, fix the support piece and give it to charity....he hates it. It takes up a lot of space in our 95sq m flat but as the downstairs is openplan and 60 m it sits beside the balcony door and for me, has been space well-used over the past almost 4 yrs...
S x