What It Did and Did not explain.
What it did explain:
How Han met Chewie.
How he got his last name.
Meeting Lando, and their strange friendship.
Obtaining the Falcon.
Why the Falcon was so trashed when he had it, but when Lando owned it, it was really nice. Also why the Falcon didn't have an escape pod.
The Kessel Run.
Hearing about Jabba and Tatooine.
What It didn't Explain:
What kind of pilot was he in the Imperial Navy. And why was he kicked out. And why did he end up in the Infantry, and not wearing a stormtrooper uniform?
Did he ever see Qi'ra again? And why no mention of her ever again?
How did he start working for Jabba?
How did Lando end up in charge of Cloud City?
Who were his parents, and what happened to them?