Boxers are happy dogs, and keep their playful disposition into adulthood.
If you don't strongly prefer to have your dog's companionship as much as possible, to have him sleep in your bedroom at night and to share your activities by day, you should choose another breed. Boxers lack the extreme desire to please that, for example, a Golden Retriever has, making training a challenge, but don't let anyone tell you that Boxers can't be trained. They are creative thinkers, and would often rather do things their way than yours. Boxers need attention and occupation or they can become destructive. Basic training in obedience and household rules is NOT optional for the Boxer.