Hi M.,
Boy, I sure wish society would make us stop feeling self-conscious about kids who appear to be a little bit different than "others."
Although I have to say--it sounds like your son is pretty normal. Not all kids are extroverts or monkeys! My son is not shy, but he enjoys independent play and just recently he's become interested in Legos and playing catch (he's four). He's always enjoyed playing with stuffed animals, flashcards, books, microphones, and musical instruments (never cars or blocks). My son is not as rascally or squirmy as other boys we know (thank goodness)--he likes to explore and run around on his own, but he is more of an observer than an outright joiner. That's okay!
What is wonderful about this world is the variety of people in it! There is not room on the planet for everyone to be an immediate joiner and an extrovert--think about it--not everyone can be a CEO or a salesman or a manager or a five-star general. Some of us have to be artists, athletes, researchers, scientists, firemen, teachers...you get the idea. How boring would it be if we were all the same??
I think you will be surprised at how your son will grow and change in the next few years. Some things about him will stay the same, but not others. I honestly couldn't believe it the day that my son wanted to play with his dump truck earlier this year--he'd never done that before--and he is beginning to get the idea that you can ask kids to play with you at school (up until now, he'd always waited for others to ask him to play).
Enjoy your son--I'd say there's not a thing wrong with him!
:-) D.