In my opinion, his record cannot be defended rationally. He took over from a general who was fired for not attacking, in North Africa, then set back that general's planned date of attack. In his memoirs, Churchill says that it was impossible to replace him right after appointing him, so they had to stick with him. 

 ::The person who 'fired' the General for not attacking was Churchill - Churchill had recently halved the available forces in North Africa by sending 50% of them on an ill-fated attempt to support Greece - which was a failure. He then blamed the Generals for the lack of success in the desert and fired a number of them in quick succession. (at least a third of all British tank losses were due to simple mechanical breakdowns, often because of such simple things as lack of air filters which had not yet arrived - the need for which Churchill seemed incapable of understanding - or the absence of spare parts) If one reads books about the Desert War written by people who were there you find that the things they found most depressing before the arrival of Montgomery was the poor Staff Work, and the abysmal state of the supply situation, ie. logistics. (one A9 Cruiser Squadron had a full inventory of spares - for the A10 Cruiser). Once Montgomery took over he shook things up and the troops started getting what they needed, but this still took time and the reason Montgomery set back that general's planned date of attack was because his forces were not yet ready to do what they were being requested to do and he would not be cowed by Churchill into starting an attack which he was sure would fail - which is what the previous Generals had in fact done.  

 ::Churchill liked to think of himself as a military genius and strategist, but he wasn't - the words Gallipoli and Singapore come to mind as examples of his 'genius' (along with the sending of the Prince of Wales & Repulse to impress the Japanese), and when you read the memoirs of various high-ranking Cabinet members, Army, Royal Navy and RAF officers, you realise just how much of their time was wasted in trying to dissuade him from reckless and ultimately pointless enterprises.