I agree Stuart is overrated, but in a very specific way. Stuart's reputation was made by riding around McClellan twice. Those rides provided useful intelligence, but that he didn't get caught on either reflected the poor organization and inadequate numbers of the AotP cavalry as much as anything. The rides inflated his stature, as did his death making him a Confederate martyr.
That said, being
overrated doesn't necessarily equate to being
bad, and that's certain true with Stuart. He was an A- who believed himself to be A+ and for a long time was perceived as being A+++.
I think
@J. Stanley offered an excellent appraisal. I'll add that Stuart was a little too much of a gloryseeker for his own good, but never as foolhardy as Custer. Even his Gettysburg ride is quite understandable, and netted a pretty substantial boon in terms of the wagon train he captured.
Stuart was one of the most well-rounded cavalry officers of the war. He didn't consider any aspect of cavalry service beneath him - unlike Forrest, Wheeler, or Morgan who were good-to-great fighters, but frequently insubordinate and resented being asked to do anything besides raid and fight. Stuart was the reason the ANV had the best cavalry in the Confederate Army. He built a cavalry corps that was able to frequently stall Sheridan in 1864, despite Sheridan's advantages in numbers and equipment. Hampton may have ended up better in the end, but he started with zero cavalry experience and no doubt learned a great deal from Stuart.
Is there any cavalry general, on either side, that can be reasonably argued as being better than Stuart or Hampton? Wilson seemed to have gotten pretty good by 1865, and Buford or Merritt warrant consideration, but I wouldn't rate them above Stuart and (by 1864) Hampton. Minty did great in 1863, but was practically invisible in 1864. By 1865, Sheridan had mastered the use of combined arms, but his cavalry excelled in 1864 only when he fought the B-team in the Shenandoah. I've already noted why Forrest, Wheeler, and Morgan aren't in contention. Van Dorn had one good raid, but most of his combat service was failing in command of small armies at Pea Ridge and Corinth.
As a tactician, Stuart was very good at using his horse artillery in any action. His horse artillery did good work at Nicodemus Heights during the battle of Antietam and the battle of Fredericksburg.
In my early years on CWT, I asked whether the Union Army even used horse artillery. Stuart's use of it horse artillery outshone anything the Union did - at least in terms of posterity.