My 5 year old loves these. They've been the first toys that he's spent hours playing with on his own, creating lots of adventures. Yes, you do run the risk of getting duplicates - I've spent what feels like hours in the shops feeling packets and then sneakily opening them up as there always seems to be 2 figures that you cannot distinguish just by feeling (similar to the lego mini figures and the Dr Who ones), which is a bit frustrating. However, I have sold my duplicates on ebay and more or less got my money back. Worth it for the amount of fun.
Surprised by another reviewer's comments about the cost - the cost is the same as the Lego figures, but these seem to have more scope for subsequent play. They are compatible with the Lego figures and the equivalent Dr Who ones, which widens the possibilities of games of goodies vs baddies! Plus they are small enough to carry in the bottom of your handbag on days out.
Can't wait for Series 2.