To attempt to analyze the strengths and weaknesses of To Kill a Mockingbird, or any other novel, would be tantamount to writing a critical essay rather than answering a single question. It is eNotes policy for educators to answer only one question per posting. Therefore, I will offer only my personal opinion about one of the strengths of the novel and leave it to other educatiors to discuss other strengths or weakness if they should care to do so. If not, you can always submit separate questions about strengths and/or weaknesses. I think you might get more help if you were to ask, for example, "What do you think is the main strength of To Kill a Mockingbird?" or "What do you think is the main weakness, if any, of To Kill a Mockingbird?"
In my opinion, the major strength of the novel is in the author's depiction of a young girl growing up in a small Southern town during the Great Depression. Scout is an interesting, sympathetic, and believable character. She reminds me of Tom Sawyer in some respects. She is smart, observant, independent, and somewhat rebellious. I feel sorry for her because she is the youngest of the two children and has to be bossed around and often verbally abused by her big brother, whom she adores. I sympathize with her need for love from her brother and from her father, and with her resistance to all the busybodies who are trying to change her into something she is not. I am interested in her thoughts, feelings, perceptions, and most other things about her, including her problem with gender identification and I guess just her problems with growing up. All of this is engaging because Harper Lee is writing truthfully about her own growing up in her own hometown. Scout is more interesting and more sympathetic, in my opinion, than all the other characters in the novel put together.