The Hobbit Trilogy was what Tolkien originally wanted Bilbo’s tale to be: an epic adventure. His publisher made him rewrite it as a children’s book. Also, much of the stuff that wasn’t in that children’s book was described in the LOTR Appendices. Gandalf did indeed go to Dol Guldur to check it out.

Honestly, the only bit that I hated was the Worms.