This is a genuinely contested question where reasonable people disagree based on different values and interpretations of history. Let me lay out the actual debate rather than pick a side for you.
Arguments that NATO has been beneficial:
•Provided collective defense that arguably deterred Soviet/Russian aggression in Europe for 75 years
•Created a framework for European stability and integration after WWII
•Member states haven't fought each other, which was a founding goal
•Some argue it enabled the security conditions for European prosperity and democracy
Arguments critical of NATO:
•Post-Cold War expansion eastward is seen by critics as needlessly provocative toward Russia, potentially contributing to current tensions
•Interventions outside the North Atlantic area (Libya, Afghanistan) have mixed-to-poor track records and stretched its original defensive mandate
•Raises questions about whether it entrenches great-power competition rather than resolving it
•Critics on the left often see it as an instrument of American hegemony; critics on the right sometimes see it as a drain on US resources for uncertain benefit
•Non-member states affected by NATO actions (Serbia, Libya, Afghanistan) often have very different views than member populations
Why this is hard to answer simply:
"Good" depends on what you're measuring against, whose security you prioritize, and what timeframe you use. An alliance can simultaneously deter one conflict while contributing to tensions elsewhere. Also, judgments often split along whether someone prioritizes state sovereignty, deterrence theory, historical grievances, or humanitarian outcomes.
What's driving your question—are you thinking about a specific NATO action, the current Russia-Ukraine context, or more the general purpose of military alliances?