Interestingly, Blackadder has been in the news just recently, see http://www.telegraph.co.uk/news/10548303/Michael-Gove-criticises-Blackadder-myths-about-First-World-War.html

Whilst it is quite sarcastic it does ring a few homes truths - commanders/leaders did put themselves some distance from the front line. Neither side really knew how to deal with trench warfare, it was reasonably new and the stalemate was hard to break. The Blackadder character sees the futility in this and displays a lack of confidence in the army commanders. I am not sure this was a prevalent attitude amongst soldiers but generals/commanders were often the butt of jokes and sarcasm in the comics of the time like Punch.

Blackadder's character is maybe more to show the harsh reality of WW1 trenches compared to the jingoism of George who is always ready to "Teach the boche a lesson". The attitude George had was very common at the start of the war, the men were proud and thought they'd "be home by christmas" (this turned in to a rather bitter joke as the war dragged on). As the men saw their families, friends, work colleagues killed for no benefit their attitudes changed and began to appreciate the full horrors of war - many expressed this in poetry of course.

The dislike of Lord Flashheart is again exploited for the sake of comedy, but from what I gather the RFC weren't appreciated by ground troops very much, believing that the pilots of the RFC had it easy sleeping in warm beds at night and flying around, out of harms way from the bullets and artillery on the ground. This was also a class thing - RFC pilots tended to be upper class, as flying had been a pastime of the rich who would afford the planes and to learn to fly before the war. Army troops were quite often working class, conscripted from their jobs in factories etc.

There is a program about the making of Blackadder, the producers, writers and actors revealed that when they recorded the final scene of the last episode many, if not all of the people on set were crying because of the atmosphere and emotion of the moment, no doubt their thoughts going to back to the soldiers who had to do it for real in battle such at The Somme.

TL;DR Blackadder is a comedy, so everything is rather exaggerated, but it does use well known attitudes/opinions and situations of the time as its basis.

I was surprised not to find this mentioned on the wiki of common questions.

Amazingly, Blackadder does not come up frequently here - I found only 3 posts mentioning it. Anyway, there's the one that seems relevant here:

How effective was British military and political leadership during World War 1? (more detail in comments)

/u/nmw had an excellent post on Black Adder and other works that have created perceptions of the war that are inconsistent with current understanding of the history.

Allied command had a tendency to be incompetent in WW1 which is portrayed in Blackadder. It actually features General Haig in the show, who is famous for his big push at the Somme, where in the first day, due to poor planning, the British suffered 60,000 casualties. Of the battle Charles Surt University says "despite this disastrous start for the British, Haig persisted with his strategy of attrition for another four and a half months until Beaumont Hamel was captured in mid-November. It had taken several months to achieve what was supposed to have taken only several weeks. General Haig's "Great Push" on the Somme had become the Great Slaughter, where British, French and German dead amounted to over a million." Wade Davis writes in Into The Silence "to guarantee discipline and order, Haig insisted that the advance on the German line be done at a deliberate walking pace." This is through no man's land that we are speaking of. Karl Blenk, a German machine gunner with the 169th, wrote "if only they had run, they would have overwhelmed us."

Haig also personally wrote "I believe in the value of the horse and the opportunity of the horse in the future are likely to be as great as ever. Aeroplanes and tanks are only accessories..." He held fully 50,000 Calvary in reserve behind the front line to exploit a breakthrough that never came. Haig never once visited the front, or the wounded. His son later justified it as "he felt it was his duty....these visits made him physically sick".

The Germans were also well aware that the attack was coming, as Haig always attacked at 0730 after the cessation of a cannonade, and the big push was much talked about in London, publicly.

From the times on July 3, immediately after the start, "Sir Douglas Haig telephoned last night to report that the general situation was favorable...Everything has gone well". This is immediately following 60,000 casualties, and not a single major objective achieved. The Daily Mail wrote "The very attitude of the dead, fallen eagerly forwards, have a look of expectant hope."

With all this taken into account, it's easy to see why Blackadder portrayed the situation the way they did. Even to this day the British Secretary of Education takes the same "sweet and glorious it is to die for our country, Britain was in no way culpable" attitude. Many of the direct quotes I used seem like they could be straight from Blackadder, they seem so silly and narrow minded." Wade Davis also mentions in his book somewhere that the British, specifically Haig didn't believe in the machine gun, while the Germans embraced it. If I find it I'll direct quote it.

Edit: found it!

From Into the Void "A survey conducted in the 3 years before the war found that 95 percent of officers had never read a military book of any kind". "As late as March 1916, after 20 months of fighting, Douglas Haig, the British commander in Chief...sought to limit the number of machine guns per battalion, concerned that their presence might dampen the men's offensive spirit. For similar reasons he resisted the introduction of the steel helmet, which had been shown to reduce head injuries by 75 percent." You really can't even make this stuff up.

Sources: http://hsc.csu.edu.au/modern_history/core_study/ww1/somme/page85.htm

Into the Void by Wade Davis