When I first opened the package for the Cookie Monster costume, I was a little dissappointed.  It looked cheap, and it wasn't "fuzzy" looking like Cookie Monster.  But it was very adorable once my son put it on.  And he was the only Cookie Monster we saw on Halloween.  A few little kids came up to him and wanted to see Cookie Monster.  Very cute!
My son was 22 months old at Halloween, and the 2T fit him well with a little extra room.  He's 50th percentile for height and weight.