Tony Inglis, in his excellent introduction, notes that The Scotsman on the 1818 publication of The Heart of Midlithian stated that it contained "the best and the worst" of Scott; nail hit firmly on head here. The opening scenes of the Potreous riots and their fallout in early 18th century Edinburgh are vivid and breathtaking. The depiction of family life and the strict Presbyterianism of simple folk are by turns enlightening, funny, and full of pathos. The characters are wonderful. Jeanie Deans' love for her sister is, like the courtroom scenes when Effie relieves the loss of her child, heart-breaking. The ripping yarn cmponents of Scott's works are all there with the riots, the outlaw on Arthir's Seat, and Jeanie's perilous trip to London. But he is often long-winded, adds in completely unnecessary and pointless scenes, relies too much on coincidence, and goes on for a good 100 pages after the glaringly obvious point for the denoumont (Inglis points out the theory as to why this is so.)All in all this book is thouroghly deserving of both its praise and its criticism but I can't help but give it five stars because, at his best, Scott is among the best storytellers I have ever read.
A quick view of the reviews here of Scott's other works confirm that he is indeed the Marmite of classic literature (here I will note in a petty manner than I don't understand why Jane Austen being good necessarily means that Scott is bad). The disagreement is nothing new. While Mark Twain accused Scott of the most awful prose and went on to blame him for the American Civil War Scott was praised to the high heavens in his own lifetime by the likes of Goethe, Lermontov, and Pushkin (the latter more or less blatantly rips off The Heart of Midlothian in his masturful 'The Captain's Daughter). What I'm trying to say is try it, see which side of the fence you're on!