The Sherman was/is indeed an amazing vehicle.
While it's tendency to ignite was never fully solved it was hugely improved by the introduction of the 'wet' stowage.
Mobility, firepower & protection are always cited as the key factors in vehicle design but there are others and in a WW2 context a primary consideration was manufacturing ability, given it's exceptionally short development time the M4 was a major success in this area, an
extremely reliable vehicle (as illustrated by the many very early variants that can still be seen in pictures of Normandy) that was also very straightforward to mass produce. Talking to veterans they are fully aware of the shortcomings of
their vehicle but still hold a great affection for it.
If not the Sherman then what else?
While it would have been nice for the engineers to wave a magic wand and produce a Tiger-killer. One must bear in mind that Germany began work on the Tiger with the DW1&2 as early as 1937 They were busy building up and preparing for war. They and Russia (with whom they cooperated greatly on such matters) were considering all aspects of armour design in some depth while the future allied nations had largely allowed the armoured concept that they had given birth to to wither on the vine. Look at the pottering indecision shown by the British and the almost complete lack of interest by the USA to underline this. Pre-war American armoured foundations were 'one man and his dog' setups.
Considering all this it is amazing that a design emerged that proved itself reliable, adaptable and long-lived. How many other class 1 AFV's served for so long from Alamein to the 80's in such diverse geographical areas? The Israeli's were able to cobble together Shermans made from scrap parts & whatever guns came to hand, (one of their parts sources was vehicles that had been dumped in the sea), the examples made from these bits of junk were no less reliable than any other. The chassis has carried an unbelievable amount of second line weapons and equipment. Variants were designed that could be manufactured by
any engineering firm with some experience of producing large objects. Not many other vehicles can make these claims to fame, especially ones that were produced from a virtually blank slate in time of war.
As Dani touches on Doctrine & training were key factors. Armies that have operated Shermans and used them in an
appropriate and thoughtful manner have had great success with them.
A much maligned and misunderstood vehicle that stands alongside the Churchill as hugely underated in the more 'glamourous' shade of other designs and deserves far more respect than it is often allowed.
errr..
I'm off for a lie down now.
Cheers,
Adam.
British Sherman 1 (Codenamed 'Swallow' as a new weapon) Alamein 1942: 
Israeli M51, 1973: 