Maybe it's just me, but it seems like the battle for Italy doesn't seem to get as much attention as other areas of World War 2. Normandy and Stalingrad are more theatrical... larger-scale clashes and deceptions. The war in the Pacific is primarily naval, and aviation plays a bigger role, so those are both glamorous, and they involve cultures seemingly more "exotic" to Western readership.
As stated above, this is the best book I've read on the subject... actually the only book I've ever read exclusively devoted to this subject, and it does a solid job addressing a few deserving main topics:
The Italian Campaign as "battlefield laboratory"
Italy is smaller scale, and was a testing ground for a lot of things that followed, so there are a lot of humiliating missteps... but they were worth it, because the lessons learned helped win the war in other places. The "laboratory" of the Italian campaign involved the first large-scale mechanized amphibious landings in the modern era (the Romans apparently did a lot of this, and the various British and American Generals involved read extensively on those. The book furnishes some of the titles, if you wish to pursue this.) Landings in Gela, Sicily and Salerno, near Naples were successful in that they weren't catastrophic failures (e.g. the landing armies weren't pushed into the sea by defending Axis powers), but were also filled with a lot of embarrassments... supplies lost overboard, equipment ruined by sand and saltwater, the hazards of landing supplies in poorly-chosen order (e.g. landing field guns to defend the beach, but with all the ammunition in another ship scheduled to arrive a few hours later; landing unarmed medical personnel before infantry to defend them, etc)
How best to coordinate multinational fighting forces? The Italian campaign was fought by American, British, Canadian, Australian, Indian, and New Zealand forces. Later some additional nations added to the effort (French North Africa, South Africa) Working out the command structures took a lot of adjusting, and some of it was complicated with the individual personalities involved (British General Montgomery was a showboater but very risk adverse; American General Mark Clark was very competent but very politically minded and not-so-secretly an Anglophobe; British General Alexander was strategically sound and aggressive in a good way, but perhaps not the best manager of his subordinates, etc) The books does well in this area... and provides a nice balance of telling the war from the flag-rank level (where the decisions are made) as well as the "boots on the ground" experience of the footsoldiers. What I particularly like was the amount of time the author describes a soldier based on his letters home, diary entries, hospital notes about him, etc, and then cuts his narration short with a "he died later that day, in an enemy shelling" etc. The cumulative effect of these thumbnail sketches, where the person becomes humanized, followed by a quick and inglorious death- really drives home the human cost of this campaign. More than 50,000 Allied fatalities (about the same losses as America experienced in the Vietnam War, but that was drawn over nearly 10 years, as opposed to 15 months here) and over 200,000 wounded in final tally.
The other big area where Italy served as "learning curve" was appreciating the uses and limitations of airpower in a land campaign. In the Pacific, airpower was supreme... because the distances are so great, because the fighting platforms (battleships and attack submarines) are so much slower than aircraft, and because the wide open sea provides clear appreciation of the targets. In land warfare, air superiority is also necessary (witness American destruction of Iraqi forces before we ever entered ground phase, in the First Gulf War), but there are a lot more places to hide, and the enemy can blend in with the civilian population, making them a poor target. The enemy might also do ingenious things like hide tanks and field guns in train tunnels or mineshafts, etc. Directing air power to good effect is trickier... which author Rick Atkinson deftly describes.
Interesting: because so many of these issues were unresolved at the onset of the Italian campaign, Atkinson argues credibly that the reclamation of Italy is the portion of WW2 which most resembled WW1... entrenchment, large scale head-on infantry confrontations, with massive body counts for small gains of real estate, and tanks (instead of air power) serving as the primary forward destructive force.
Political aspects of the fight
What's interesting about the political dynamics of this theatre is that Italy was an enemy at the time of the initial Sicilian landing, but by the time the Sicilian operation was completed, Mussolini was driven from power, and his successor, Marshal Pietro Badoglio, promptly surrendered. Now, officially, Italy was essentially an ally being occupied by hostile German forces... but it wasn't that easy, because pockets of Italian fascists were still fighting, and a large portion of the civil population was ambivilent/ noncommittal to the fight. This complicated a lot of supply questions. If the local population is willing to help supply you (i.e. sell to you), that reduces the supplies you need to bring to an operation, and how much you care about defending your supply chain. This is also an area rich with psychological warfare, and a robust campaign was mustered to convince Italians to support the Allied forces (even fight the Germans with them), and to disrupt German operations. As the campaign progresses, the Italians come over, but the question of loyalties is still a factor in the landing at Salerno.
Other considerations explored
How much value is there in capturing Rome? It has great propaganda and morale value, but much less industrial value than pushing on for a quick capture of industrial centers in Turin, Milan and Bologna.
Arguments pro and con for invading Italy at all. Was it really necessary to the war? Churchill really wanted to secure the Mediterranean, in hopes of reestablishing trade with India through the Suez Canal... in a desperate and ultimately unsuccessful bid to retain the British Empire after the war. Americans were less enthusiastic, and felt Italy could be marginalized and left to "die on the vine", thinking that a landing in Southern France might be more effective, by forcing a direct confrontation with German border forces earlier in the war.
Ultimately, the decision to Italy came down to two factors: 1) and urgent need to draw German forces out of the Russian theater, to ensure that Russia not fall to Hitler (although there is a question of whether he could have held it, even if he captured it); and (2) insufficient capacity to transfer the land forces anywhere else. Neither the British or American Navy could spare sufficient transport ships to more all the tanks, infantry, and mobile infrastructure which captured North Africa in 1942 to the Pacific, or even up to Britain to participate in the Normany invasion. Tunisia is only about 125 miles from Sicily, so the jump could be achieved over this small distance with many short shipping runs, but would be impractical for much larger distances. Really, if the forces left over from the North African campaign weren't used to capture Italy, there was no good place to locate them, with the available shipping resources. Even in the European theater, WW2 was truly a naval war.
Good reading. Four stars (not five) because it gets too bogged down in detail in some parts, is a bit too uncritically laudatory of Eisenhower, and it lacks sufficient maps to support the text. Some of these little villages are not in my atlas. Google maps makes up for some of it, but even so, there are bridges, reservoirs, railroad lines, etc which aren't around today... a five star military history book would err on the side of too many maps, rather than too few.