I would have to say that overwhelmingly, imperialism had a positive effect on the world. Of course, there are huge exceptions to this, mass murders, genocide, persecution, exploitation, and so on. All of those terrible downsides pale in comparison to the benefits of bringing modernity to the world (assuming we mean 18th and 19th century European imperialism) and all the lives it saves, rights it provides, standards of livings it increases, etc.
Now, even though I think that the effects of imperialism are on average overwhelmingly positive, it was still wrong. It’s wrong to force yourself on other nations and make them adopt your ways, even if it is for their benefit. You can do bad things that have a good outcome. That is why we must always ask: do the ends justify the means? I don’t think that there is a simple yes or no answer to that. It was wrong for European nations to conquer, control, and exploit other peoples of the world - yet if we look at lands untouched by colonialism they are mostly living in the same terrible conditions that prevailed there for thousands of years, living under despots far worse than almost any European king.
So we shouldn’t demonize Europe for Imperialism or scapegoat them for the problems of modern this world nations. Europeans were only doing what every other people does given the opportunity, just doing it better.
Would I advocate for future foreign policy with imperialism as a model? Absolutely not! I’m for leaving the rest of the world alone.