The general shorthand for Jonathan Strange and Mr Norrell seems to be “Harry Potter for adults”, but as the only common element is magic you might as well call it “the Paul Daniels Show in book format”. The immediate comparison that springs to mind for me is Neal Stephenson’s Baroque Cycle (Quicksilver, The Confusion, The System of the World), though that still doesn’t stretch much past that they’re both dense, weighty historically-set tomes. The Baroque Cycle is set in the 17th and early 18th century, has strong picaresque elements, and focuses on science and technology, whereas Jonathan Strange and Mr Norrell is a Regency novel from a 19th century where magic exists.
Jonathan Strange and Mr Norrell is extensively footnoted with references to magical texts and happenings, which was initially slightly irritating and disruptive, but it builds such a cohesive, believable world that the magical becomes matter-of-fact, a natural part of things. Though the pace is measured, and at times there isn’t an awful lot happening, it doesn’t happen with such style that it carried me through. Not quite “I couldn’t put it down” (apart from anything else your arms need a rest now and again), but most enjoyable. Recommended, especially if you like Regency novels featuring magic.