There has been constant discussion over the years over Guderian's role in the creation and development of Blitzkrieg, itself a term coined by American journalists and never by Guderian himself. Let's look at the common questions one by one:
1) Guderian did not invent Blitzkrieg alone as he borrowed from other theorists
This is partly true. As with all good ideas no one person thinks of it alone. Thus the British theorists J.F.C. Fuller and Captain B.H. Liddell Hart (although his role is now questioned) and also Charles De Gaulle were also exploring the ideas of using a massed concentration of tanks to achieve a decisive breakthrough into enemy lines. According to David Glantz and Jonathan M. House in
"When Titans Clashed: How the Red Army stopped Hitler", Soviet theorists too were examining the possibility of combined arms tactics but the Soviet purges of 1937-38 robbed the Red Army of most of their forward thinkers. The Civil War Commander M.N. Tukhachevsky and the military theorist V.K. Triandafillov were in principle at least examining tactics that were remarkably similar to those of Guderian.
The key fact that separates Guderian from all of the above however was that he was able to put theory into practice. A great deal of the reasons for this is down to Hitler, who was able to see Guderian's vision and granted him the authority and resources to shape Germany's panzerwaffe. Guderian was also a pioneer of using radio in military applications, which was essential for the close coordination of panzers and the supporting Luftwaffe to take place. Guderian also proved remarkably effective as a field commander.
There is also the issue that 'Blitzkrieg' was just a development (or reinvention) of earlier theories such as 'Vernichtungsschlacht'. Again this would be hard to avoid IMO as Guderian, having served in WWI, would have been exposed to earlier tactics and been influenced by them. A good example of this is how the German WWII tactics of 'Elastic Defence' were really just an evolution of the same tactics used by the Imperial German Army. Of course, no matter how much tactics change some truisms still remain, such as the need to encircle and destroy enemy armies in the field. A good example is the huge encirclement at Kiev in July 1941, where after the initial Blitzkrieg tactics had allowed German panzers to achieve breakthrough, a massive Vernichtungsschlacht was conducted locally to destroy and capture nearly 700,000 men. Essentially, there were 2 phases to Blitzkrieg. The first stage being the panzer breakthrough and the 2nd, more traditional, stage resorting to more traditional methods such as Vernichtungsschlacht. Some argued that the need to conduct Vernichtungsschlacht to reduce the many pockets that had been created by the rapid advances of Blitzkrieg cost Germany their speedy advance towards Moscow in 1941.
2) Guderian was an ill-disciplined commander who was reckless and foolhardy
There has been a lot of discussion regarding Guderian's supposed lack of discipline. It didn't help that right from the start he was seen as an outcast and a troublemaker by the inter-war German Generalstab. This was mainly for the fact that a) Hitler was giving Guderian's ideas a lot of attention and b) that the influence of the traditional service arms, artillery, infantry and in particular, cavalry, was being eroded as a result. Most of the Generalstab could not 'get' Guderian's ideas and called much of what he proposed as folly. These clashes of ideas and understanding would follow Guderian into war. Guderian clashed with Paul von Kleist on 16th May 1940 during the Battle of France when the latter, who was Guderian's direct superior at the time, ordered Guderian to halt his panzers at the Meuse River so that the supporting infantry could catch up. Guderian refused and advanced 80 kilometers into enemy terrority. When Kleist caught up with him he was sacked on the spot but Gerd von Rundstedt, overall commander of Army Group A, refused to authorize Kleist's actions. Kleist, as he later demonstrated in Russia, was one of those who never fully appreciated the use of armour as laid down by Guderian. Guderian knew he was correct and although he disobeyed a direct order he did so for good reason. After all, this was in line with the German tradition of 'Auftragstaktik', in which officers at all levels were required to think for themselves and not merely follow orders.
A similar charge was labeled at Guderian during Operation Barbarossa in 1941. This time his commander was Field Marshall Gunther von Kluge, another commander who did not really appreciate the operational use of panzers. There is some confusion as to what happened on December 25th, 1941. Kluge gave Guderian an order to stand-fast in accordance with Hitler's orders. Guderian ordered his 2nd Panzer Army to begin a tactical withdrawal to better defensive positions but still in line with Hitler's general orders. Kluge (who was later to challenge Guderian to a duel) accused Guderian of insubordination and sacked him on the spot, which Hitler authorised. Thus ended the field career of one of Germany's finest commanders.
3) Guderian's conduct during the War
There are a couple of gray areas regarding Guderian's conduct at key points in the war. The first was his acceptance of a country estate in Warthegau in what is now Poland. He also accepted a pension from Hitler. My opinion is that it's easy to be judgmental in hindsight but Guderian had fought hard and long for his country and the estate was in what was considered East Prussia of old. Why shouldn't he have accepted? There was also the charge that Guderian threatened to shoot prisoners at the Battle of Wizna during the Polish campaign, but many historians saw this as merely a bluff to get the local commander to surrender. Certainly there is no evidence that Guderian really intended to shoot prisoners.
His 2nd gray area was his conduct during the July Bomb Plot on 1944, where Guderian knew of the conspiracy, declined to take part and 'took a walk' around his estate on the actual day of the plot. Again with hindsight it's easy to be harsh with Guderian but again he must have been experiencing a huge dillema. He was, after all, a professional soldier and not a politician. Plus he was also being smart and selfish. Had the Plot succeeded he would have been well placed within any new regime. This is the one time where Guderian 'fell down' within his personal character but he was being smart, rather than absolutely loyal to the man whom he had sworn an oath of allegiance. Guderian had a family to think of so one can hardly blame him for thinking of them rather than his führer.
Bibliography and Links:
David Glantz and Jonathan M. House, "When Titans Clashed: How the Red Army stopped Hitler", ISBN-10: 070060717X
Kenneth Macksay, "Guderian: Panzer Leader", ISBN-10: 0306811014
http://en.wikipedia.org/wiki/Battle_of_France
http://www-cgsc.army.mil/carl/resources/csi/wray/wray.asp#elastic
http://www.bevinalexander.com/excerpts/world-war-ii/new-german-military-system.htm