Montgomery is the subject of widely differing views as to his competence; these views seem largely to vary with nationality. In the US, as far as I can tell, Monty is seen as overly cautious; his unwillingness to begin an attack before achieving overwhelming superiority of forces is seen as a sign of weak will. In the UK this caution is seen as part of his great concern for the welfare of his men. Incidentally achieving an overwhellming superiority of forces has since become standard doctrine for the US!
IMO the British Army of the Second World War was better led than at any time in its history. Almost without exception, its senior officers were professionals, selected for ability rather than social background, and veterans of the slaughter that was the Western Front in the Great War (I use their own term for the First World War). They had seen the massive losses caused by bad command decisions, and just how badly things can go wrong when you trust to luck. They had also seen the devastating effect on the country by the loss of the larger part of a generation of young men- even in a victorious war.
It is ironic that in Market Garden, when Monty finally gambled- he lost. It should not, however, tarnish his reputation, or the reputation of the other British generals of that war.
Please note: I am not a historian, except on a purely amateur basis. All the above is purely opinion. If anyone challenges my view on this subject, I would be interested to hear their view- either in this thread or as a PM.