I have the Illustrated Classics series, or at least a great many of them. I have read them, as well. I found them to be “dumbed down,” IMO. I was in high school when I read most of them, on my own, not for school. I am an avid reader, and I found them interesting, but at no more than a 6th – 8th grade reading level, maybe even younger than that (now I can’t remember). I have been collecting the original, unabridged classics for the last several years, and as I’ve read them, I also found that there are parts of the story that gets left out in the abridged versions. Granted, they take out bad words and bad situations, but then where is the value of the story if you can’t learn from characters’ mistakes, kwim?
Anyway, that’s my 2 cents.