Of the series, I find that "Chamber of Secrets" is better as a series book than standalone. I recall the first time I read the book it did not immediately capture and hold my attention like the first book did, but it was still a fun read and I enjoyed getting to share the story with my kids. Below I'll outline what I liked, didn't like, and what I find important to take note of in this book. There will be spoilers, but I'll do my best to use Harry's invisibility cloak where possible.
What I liked: Dobby. The Burrow. Professor Gilderoy Lockhart. "Eat Slugs". Hagrid. Sir Nicholas De Mimsy Porpington.
For me, the saving grace to the entire book was the absurdity of Professor Lockhart, the dedication of Dobby, the warmth of the Burrow, & the merit of who someone becomes vs. that person's origins.
What I Did Not Like: The inhumane treatment of Harry (by the Dursleys) and Dobby (by everyone). Also, while harsh, the second book felt like it was trying too hard to mimic the first book & therefore fell a little flat for me. Any sequel following a smash hit will always be judged harshly, so perhaps if this was to be the "dud" then it was a good one to choose. I just had a hard time really getting into this book and kept finding myself reading other books at the same time.
Lessons Learned: Always be wary of information given when you do not know the information source. Treat others as you would wish to be treated. Only you determine who you are, not your circumstances (how would you compare/contrast Harry Potter and Tom Riddle?).
Important nouns to note: Dobby. Ginny. Tom Marvolo Riddle. Polyjuice Potion. Parsetongue. Acromantula. Heir of Slytherin. Fawkes. Sorting Hat. Sword of Godric Gryffindor. Everything in Borgin and Burkes. Basilisk Venom.