I would argue, in the strategic sense, the crusades were very successful; it is very possible Christendom would have been lost without them.
First one must place the crusades in their proper context. They took place in the middle of a 1000 year long war between Christendom and Islam. After the loss if the Middle East and North Africa, and until the crusades, the war was largely a defensive war fought against Islam on three fronts: Iberian Pennisula, Sicily/ Italy, and into Europe via Asia Minor. The Crusades were the first attempt to turn this defensive war into an offensive war; and at the same time securing lands of great cultural importance to Christendom.
The result was that the greatest Islamic general of all time, Saladin, spent most of his career fighting Christians in the Holy Land instead of invading Europe. That man was going to be successful at whatevere he did, so it’s good that he was kept occupied elsewhere.
In addition, they stopped large military migration of Islam from the Middle East into Spain and which pretty much set the pattern that the Moors were responsible for defending Spain from that point forward. Allowing an eventual victory a couple of centuries later.
From that point on, the Arabs never again were willing to commit vast armies towards the invasion of Europe without holding some in reserve ( certainly a change in behavior from the first 3 centuries of Islamuc advance.
Finally, Christendom learned the necessity of fighting the war at times from a strategic sense, drawing forces from across countries at specific times, which proved decisive at Lepanto, and twice at Vienna.
Yes, Islam still made significant inroads after the crusades, notably the eventual conquest of the Byzantine Empire. But that was largely due to the continual internal weakening of that Empire, and it was likely delayed for 3 centuries due to the crusades.