I very much enjoyed Toy Story 4. I thought it was good, and I think it doesn't at all "undo" the perfect ending that the third entry gave us, which was a legitimate fear some people had. What I will say however, is that I don't understand just how much most people seem to have loved it. I have seen multiple people say it's the best of the four, and I more think it's the... worst. That's not a knock! This is a seriously good series (and also I think it might actually be either better than or maybe as good Toy Story 2). But I am not quite feeling the overwhelming positivity that it has garnered from a lot of my peers.
Final rating:★★★ - I liked it. Would personally recommend you give it a go.