Abhimanyu was one of few warriors who knew how to enter the dreaded spiral battle formation and reach its center, although he lacked the knowledge of breaking the formation and exiting it.
He always represents two things for anyone reading the epic Mahabharata:
1) Someone so courageous and capable that it took all his enemies combined to surround him on all sides, separate him from his allies and finally take him down.
2) Someone who had incomplete knowledge on how to face a particular problem but decided to tackle it head-on instead of researching further or planning for a backup because he felt it was too cowardly to back down.
His enemies broke many rules and he died unfairly. But his death made his team realize that in order to win, they also had to break free of the established rules and think creatively to tackle the complex problems they faced. It also gave his team the drive to avenge his death that eventually led to their victory.