This is a very interesting question, and I've often thought about this. Now, I'm simply going to analyse this from the point of view of who Calvin currently is, as a child.
1) Calvin's current perspective of what he wants to be as an adult
This has been portrayed in quite a few of the comics. Calvin appears in several strips as an adult, often when he's been roped into playing make-believe with Susie, and the comic itself is drawn in a much darker and more realistic art. For a while, he consents to play with her, (during the course of which he is bickering and making snide remarks) until he finally breaks and reveals the much darker side of his that he is so fascinated by.
2) A romantic
Now, you might find this extremely hard to believe, but bear with me on this. Deep down, Calvin likes Susie a lot. He goes out of his way to 'interact' with her, albeit in a very annoying way. It is quite clear though, that Calvin cares for Susie, and his means of annoying her is just his way of telling her that he likes her.
3) A Happy Person
By happy, I'm not just referring to him being a broken down lazy oaf who is content idling away. Calvin is going to find that one thing that he loves to do and will go on to pursue it and remain happy unlike a majority of us who are stuck working at jobs simply to make a living. Look at the comic strip below. Hobbes is essentially a figure that voices Calvin's thoughts and emotions. You get the idea.
4) Someone who values his best friends.
I know it's true that a lot of the comic strips have depicted him as wanting to be someone who is adventurous and merciless (especially towards Susie). But don't you make the mistake of believing that he would sell out the ones he loves. He cares about everyone around him, and will go out of his way to make them happy.
5) A Successful Person.
He may not end up topping his class in high school or college, but he is going to end up successful. Big time! He knows how to get things done his way and will persevere to accomplish his goals.
6) An educational reformist.
Calvin hates the educational system. And rightly so. He believes that the stuff they are taught in school is in no way going to help them in their future lives. He believes in a more practical method of teaching, one that will enable to actually live their lives they way they ought to.