On their own, the Italians had they best successes in the Mediterranean, the centerpiece being knocking out two British battleships with a special forces operation in December 1941. They made a pretty good scrap in the Med, and for a while were winning in the center, allowing the lines of communication to Libya to continue pretty much unhampered by the Royal Navy, and making supply runs to Malta a little dicey.

In Africa, I personally consider the Italians to have been given short shrift. Axis forces in North Africa generally numbered about the same as the Eighth Army, but barely a third of them were Afrika Korps. For all the talk about how it was the Afrika Korps which fought Montgomery, it was Italian troops doing a large part of the work. Near as I can tell, when the Axis won, the Germans kept the credit for themselves, and the Allies blamed those high-quality German folk: They certainly weren't going to admit they had been beaten by Italians! And when the Axis lost, the Germans would be quick to blame those lazy Italians, while the Allies were happily capturing everyone, but more Italians than Germans simply as there were more of them there. Case in point, the US Army's first major encounter with the Axis at Kasserine pass is generally viewed as the inexperienced Americans getting trounced by the experienced Germans (Which is a bit unfair to the Americans who recovered well and held the next line). The unit which broke the American line? 5th Bersaglieri, of the Centauro Armored Division. Nobody 'on the street' seems to know that the Italians were even there, let alone that they played a critical part in the fighting. Quoting Rommel, "it was an exciting scene of the tank battle north of the pass…..and I have special praise for the 5th Bersaglieri, who attacked fiercely and whose commander fell during the attack; they threw the American, British and French forces out of the pass, allowing the II/86 and K.10 to exploit the breakthrough"

This is far from saying that they were a particularly good army on the whole: their equipment was near hopeless, and unit quality varied widely, often on the slightly poorer side. For further expansion on the topic, check out https://www.reddit.com/r/AskHistorians/comments/6mfa7i/why_was_italian_leadership_so_poor_in_ww2/?st=j5or9ymv&sh=d09122d0 by /u//kieslowskifan

Personally, I'm a fan of Iron Hulls, Iron Hearts, by Ian Walker. It's easy reading, and traces the history of the three Italian armored divisions: It shows what the Italians could do if they had a mind to it.