First of all, while Germany was supported by all the resources they needed for war by Soviet Union, so they could really finish off the Britain (they lost BoB because of some stupid mistakes of Hermann Göring though) and then could easily take the Africa. With no annoying Britain and no reason to waste resources in Africa (and African oil) they could attack Soviet Union with a chance for a victory.
On the ost front - Germany had a great chance to win - while 'rasputitsa' and then winter didnt start Guderian tanks, as Guderian begged the Hitler, could attack and take the Moscow. In that time Moscow also wasnt prepare for defence and had no that 1 million army from Siberia. But, Hitler said "We cant go for a Moscow before we take Kiev, so turn your tank back" - yeah they took Kiev and surrounded another Soviet army but if they just took Moscow they really could finish the war). If Japan attacked SU on the east Stalin couldn't able to send the whole 1 million Siberian army to Moscow. It is 1 million army who highly specialised on winter war.
Germany should never declare war on US and Hitler should never take command on Eastern front - he did just huge mistakes. This guy just didnt know what to do. Sent tanks to one direction then turn it back then sent againt, made a really wide front, failed at Caucasus, didnt ordered to reatreat from Stalingrad. Then that retarded operation "Citadel" that was failed before it started.
Yeah, Germany had a chances to win the war, but they wasted it.
Speculation is always easy, just to point it out.
1. Battle of Britain wasn't failure for original plans, because in the first weeks Britain's airforce was almost completely destroyed, their airfields were almost unusable. Don't remember who said this, but some RAF general said that BoB was already lost until (Not Hermann Göring, although he was idiot too) Hitler gave the order to bomb cities not british airpower (airfield,factory,radar). This gave very important respite for RAF to fix airfields and their airpower. He did this because Churchill in some stupid/genius idea send night bombing to Berlin, which made Hitler angry and changed totally the tactics for BoB. If they had kept the original plans for BoB britains airforce would have been totally nullified and Germans would have had total air control of south&mid Britain air, like allies had in late war.
2. Hitler's total paranoia and reign over Preussian Generals made the command and decisions always get second guessed, which in the end was many times shown over Operations. Dunkirk (Hitler ordered against it), Battle of Britain (Hitler changed targets to cities and didn't keep bombing airfields), Barbarossa (Hitler decided against rush to Moscow, which his generals supported), Stalingrad (Hitler "no retreat" order + locked Germany's most powerful asset "Mobile warfare" to "Meat grinder" city fighting) there was a possibility to get Stalingrad surrounded & sieged if they focused around the city not inside it, After Stalingrad (Hitler still had order "No Retreat") which made alot of units get surrounded like the germans did to soviets. There are many war operations that started as planned, but our savior Hitler put his fingers inside and changed the plans, if Hitler had trusted his Generals from the start to end, war would have been different.
3. Italy & Mussolini. Africa was total failure for Mussolini and made Germans waste efforts & resources there which would have helped in War against russia. Balkans again made Germans intervene and made resources used there which delayed their Barbarossa plans. Italy had the most powerful navy inside mediterranean, but it's weak use of them. Made them useless and most of them were just sunk inside the harbors.
4. Strategic decisions after fall of France. Main focus on taking out Britain from the war, before even thinking about invading Russia, could have made history books different. Succesful BoB & Submarine strangle hold would have made living in that island nation hell. Just food for thought.
Why Axis lost in simple word is "Hitler". He started all and he messed alot of things in the war. 5 years could have been 6-10 years. Speculation is fun, but in the end useless. Nobody anyway here wanted for Hitler to win.