Steven Zaloga confronts this question head-on in his book Armored Champion: The Top Tanks of World War II. He points out that Wittmann can be reliably credited with about 135 kills. Of those, however, 120 of them were scored in 1943 on the Eastern Front in a Tiger I. In other words, Wittmann had the benefit of a virtually invulnerable tank with an extremely powerful gun at a time when the Soviets had yet to introduce in quantity tanks like the T-34-85 or the IS-2, both of which were capable of dealing with the Tiger and Panther on relatively even terms. He also points out that the vast majority of tank kills are scored from ambushes rather than bold and valiant head-on engagements. This, appropriately, was how Wittmann died: during Operation Totalize in Normandy in 1944, his Tiger was blasted open with a single shot from a British Sherman Firefly hidden in a hedgerow.

Complicated subject because of his low rank. For most of his actions, you will not have enough data to form any objective opinion. Villers Bocage is an outliner due to the attention it got after the war. It is not possible to evaluate most of his engagements in such detail, so to establish his personal tactical skill through the war is impossible. Given that he destroyed tanks before he got his Tiger, we can assume he wasn't bad at his job at least.

Given that he was trained to command a Tiger we can assume his superiors thought he was competent. He was already commanding a STUG III and was rather successful so he was transferred to get officers training. He later was transferred to one of the first Tiger units as a commander.

Zalogas assertion here is a bit superficial. The fact that Wittmann was highly successful with the Tiger does not devalue his performance in the Stug III. He claimed more kills during his STUG III phase than the vast majority of Allied tankers during the war. As STUG commander he saw little tank combat but still he claimed several destroyed tanks on different occasions. After that he was pulled from the frontline and later commanded a Panzer III, there wasn't much time or occasion to destroy tanks until Zitadelle. Zalogas says he only lasted two months on the west front, while technically correct he destroyed about 10 tanks in that time which would earn him a lot of praise on the Allied side. For some reason people think Wittmann became a house-hold name due to Villers Bocage, it is correct that he became the propaganda poster boy because of Villers Bocage but he already had the Knights Cross with oak leaves before he even came to the Western front. He also was mentioned in the Wehrmachtsbericht. He was an extremely successful tank commander long before Normandy and if I remember correctly the most highly decorated one. He didn't get famous because he destroyed some tanks at Villers Bocage he already had a long track record of outstanding performance.

His actions during the Normandy campaign allow for a better analysis. His Villers Bocage action made him famous and was likely the reason you have heard of him but I don't think his performance was "very good" there but mostly because he was the company commander. What happened in Villers on a tank level was impressive and had shown again that Wittmann as his crew was highly skilled and were able to deal in extreme situation with multiple targets. Wittmann's tank was engaged several times by enemy tank/gun which got knocked out soon after. This happened partly in a city and close quarters. This alone demonstrates that the entire tank crew was highly capable. For a rookie crew, it is already hard to drive slowly towards the action, spot and acquire targets and hit them within a short amount of time. Wittmann's crew drove through an occupied area with up to 30 AFVs in the vicinity and was able to knock out everything they spotted within a short amount of time. BUT Wittmann at this point in time had the command over a Tiger company, which represented an extremely valuable combat asset. Schneider and other have already debated this topic and I tend to agree. The British forward forces were very exposed and did no recon, given that forces of other German units like Panzerlehr were already approaching or in striking distance the attack looked premature. Wittmann dashed alone in a single Tiger between the strong point 213 and Villers Bocage, while this action destroyed a lot of enemy material it is questionable if not a bigger opportunity was squandered here. The rest of his unit engaged later and he didn't communicate with the first company. The fact that he attacked alone certainly shows that he was "brave" but also showed the aforementioned recklessness. The entire 101st SS was a very powerful unit, with the right support from Panzerlehr certainly able to maul the entire 7th Armoured or at least the forward elements, but Wittmann attacked alone and lost the element of surprise. The later attacks weren't that successful, how much of this was due to Wittmann is very hard to tell. As company commander, it was questionable to move in alone. As you might notice there are two types of considerations here, as tank commander he wrecked havoc and as a company commander, he might have lost a golden opportunity to seriously damage a British armoured division.

His death ride happened in a comparable manner. He commanded a counter attack into several attacking Canadian armoured regiments. The attack was doomed to fail and it did. He got ambushed and died so did his crew and most of the other tank crews involved. Here it seems to show that Wittmann was used to combat with better odds against weaker enemy guns, while his last battle is used to show his incompetency I think this is absurd. At some point, you are on the receiving end of the AP shot. But I think it's obvious that his skill as tank commander vastly exceeded his skill as company commander. His record as tank commander is outstanding and proves his skill beyond doubt but his experiences on the Eastern Front seem to have made him a rather unfit company commander. He never let a unit on the Eastern front so everything he learned about leading happened on the Eastern Front and now had to be applied to a very different situation. Getting killed during combat is likely if you exchanged fire with more than 100 enemy tanks but leading a counter attack over open terrain with 6 tanks against an opponent with about 15 times more tanks in the vicinity is foolish.

So it seems Wittmann and his crew were very experienced and highly capable making them an extremely valuable combat asset. His performance in different AFVs was outstanding. This made him one of the most successful and decorated tank commanders long before Normandy. He was then promoted and made a company commander which required a different skill set which he didn't seem to have. Confronted with a new type of warfare and more capable anti tank guns he was slow to adapt and was killed in an ill-fated attack. In the end, he destroyed ~10 tanks in Normandy for the loss of two.