Short answer:

I'd suggest that "how good was General X" warrants far less attention than armchair historians devote to it. As Napoleon once observed "God is on the side of the big battalions"; losers like to obsess about their valiant commanders . . . but they lost. The point of war is to win, and "more men and stuff" is a more frequently travelled route to victory than genius in command.

Discussion:

Rommel was a good general, in a military with lots of good generals, and more importantly, with remarkably good non commissioned officers. A more useful question in looking at the German military is "how did they come to find, train and promote capable military men?" And "why did this substantially competent military establishment enter a war of choice, which it then lost in a relatively short period of time?".

Its notable that there's far more ink shed over von Manstein, Rommel and Guderian than is devoted to, say, George Marshall and Dwight Eisenhower, or indeed Marshal Zhukov or Aleksandr Vasilevsky. And no one pays much attention to the ordinary sailors and soldiers and staff officers who made complicated things-- like an amphibious invasion-- work.

Rommel is known for his work on infantry tactics -- a book called Infanterie Greift An, based on his experience in WWI, more or less a guide to the "shock troop" tactics that Germany developed at the end of WW I. He had similar ideas about armored tactics, never got around to writing the book on them, but had a clear idea of how to use armor in modern warfare. As a commander, he's well known for the campaign in France 1940, the campaign in North Africa, preparation of the defenses in Normandy . . . but it's notable just why he lost in North Africa: not enough supplies. So when you look for the fathers of victory-- spare a little time for the Quartermaster's Corps and Ordnance. Victory comes most often to those who get to the battlefield with the most men, best fed, best fueled, best armed. A Tiger tank that's got no fuel, spare parts, or ammunition is scrap metal. Rommel himself observed

“The reason for giving up the pursuit is almost always the quartermaster’s difficulty in spanning the lengthened supply routes with his available transport. As the commander usually pays great attention to his quartermaster and allows the latter’s estimate of the supply possibilities to determine his strategic plan, it has become the habit for quartermaster staffs to complain at every difficulty, instead of getting on with the job and using their powers of improvisation, which indeed are frequently nil. But generally the commander meekly accepts the situation and shapes his actions accordingly"[1953 Liddell-Hart, ed. "The Rommel Papers"]

If you read one book to inform a less "great generals" driven view of military history, I'd recommend

Martin van Creveld, Supplying War: Logistics from Wallenstein to Patton, Cambridge University Press, 1977.

. . . it's not the "History Channel" view of war, but it is the historian's.

If you're trying to understand how the German Army came to be what it was, Gordon Craig's The Politics of the Prussian Army 1640-1945 is a classic work, very well written, that places the German army and its leadership in historical context. Rommel isn't a man who invents himself, he's the product of a military culture that's centuries old-- he's a capable example of it, but just one of many.

If you go to your local bookstore -- well, you can't, but back in the day-- you'd find the shelves groaning under the weight of military biographies, "great captains" from Alexander the Great to Marlborough, Frederick the Great, Napoleon, Robert E. Lee and so on . . . let me make the suggestion that they all matter much less. Stonewall Jackson notwithstanding, the Union won the Civil War, pursuing a strategy which is much less glamorized in popular history: produced more stuff, field more soldiers. That's pretty much how the Allies defeated Nazi Germany as well . . . "good" generals like Rommel notwithstanding.