Hello Sheena!
First of all, thanks for being a responsible caregiver and having your puppy neutered.
Secondly, you needn't worry about your friend being less playful following the surgery. The first few days after he arrives home, expect him to be somewhat quieter than normal, but that is only due to the fact that he will have been anesthetized for the procedure. They can be groggy, sometimes nauseous and sleeping more for the first day or two, but after that he should return to his normal playful self. There should be no notable change in his behavior even though he's been castrated. especially since he's a puppy. Sometimes in older male dogs you will see less aggression or dominant behavior, but that won't be a problem for him.
Also, he will never have to experience the possible problems of testicular cancer and other reproductive system conditions, and will live longer for it!
The main problem seen following castrations is licking at the surgical incision, creating a secondary bacterial infection. So your job is to help prevent that, then to enjoy your friend for many years to come.
Many thanks, and best of luck.