The spring offensive launched by the Germans in 1918 was ultimately a failure that resulted in the deaths of hundreds of thousands of Germany's best troops and the squandering of significant material resources. The Germany army found itself overstretched and was soon back on the defensive as the allies launched their own "100 Days offensive" that would end in armistice.
That said, in comparison to the major allied offensives of 1916 and 1917 which failed to capture significant amounts of territory, the Germany spring offensives captured vast tracts of albeit strategically useless country side and threw the British and French armies back 50 miles in some places.
What explains the near successes of these massive German offensives while similar allied offensives never achieved similar "breakthroughs" into open country?
Right I just lost an enormous post which handled this question directly and I'm not even going to bother; I'm sorry. I wrote a post on a similar topic here titled "In 1918, why was the Allies' 100 Days Offensive so successful, while the Germans' Spring Offensive failed?" which I hope will answer some of your questions but is mostly, as you can tell, about the offensives themselves and not comparing them to the likes of the Somme.
The TL;DR: of it all for your question though is that the allied offensives were not necessarily trying to achieve breakthrough like the Germans were. The offensives were in no way comparable because their objectives were different. The Germans were making a mad dash for Paris, the British were trying to seize this one little railway center or take out a ridge or just generally kill Germans.
We must also remember that on the basis of Hutier Tactics the Germans were using the absolute best of the best soldiers and striking the most lightly defended areas of the front. Of course they would break through. The issue came with, though, once they broke through then what? They weren't capturing major supply depots, rail centers, or HQ's because obviously there was nothing there if the allies weren't defending it very much. However once the stormtroopers broke through all that remained on the front were the least experienced troops on the front and now the stormtroopers were out of range of their own artillery and were basically on their own to be cut down by allied strategic reserves, heavy guns, and cavalry.
You're not comparing like with like. The perception of the allied offensives of 1916 and 1917 is of them failing to seize territory, as if the ground itself was the prize. Like the failed German offensives of 1918, they were aimed at knocking their enemy out, not at seizing ground. One could argue that the British offensive on the Somme in 1916 was at least a partial success; the German Army leadership clearly thought so, and believed that the battle had destroyed the cream of their Army. Despite the Brits being pushed back so far in the Spring Offensives, the necessary breakthrough was never achieved, and the Allied counter-attacks ultimately led to Germany's defeat in the Autumn. So, not much more effective at all.
As /u/splitbrain says, the Germans were able to transfer a lot of soldiers from the eastern front to the western front.
Now by a lot, we are talking about A LOT. British estimates put German strength in March 1918 on the western from at 177 divisions. To put that in perspective, at 2nd Alamein, the British Empire would field a total of only 11 Divisions!
The German blow for Op Michael would fall on British Fifth Army with approximately 14 divisions. Ranged against them were some 74 German divisions. Again for perspective, that's more divisions than the Germans had in the whole of western Europe in 1944.
The superiority of artillery was even more pronounced. The German bombardment on 21/03/1918 lasted for 5 hours during which an absolutely staggering 3,500,000 shells were fired.
Of course, Fifth Army had to fall back.
But they were falling back on strategically worthless ground. In fact, fifth army was to be so denuded of troops that for the battle of Bapaume, they only had 3 infantry and 1 cavalry divisions.
When the Germans attempted to attack the well defended and strategically valuable ground in and around the Ypres salient, Arras and Amiens, they were stopped dead. They made almost no progress at all, despite huge expenditure of blood and treasure.
So what does this mean? Yes infantry tactics, improved communication, logistics etc. helped, the fact is that artillery and overwhelming weight of numbers must be counted as the main ingredient of German success (such as it was) in spring of 1918.
It was a single shot weapon though. And once the Germans had shot their bolt and missed the target, they could not possible hope to win the war.