Yes, well, unlike The Mark of the Rani, The Three Doctors hasn't improved much over time.
What has always stood out the best about that serial is the marvelous chemistry between Jon Pertwee and Patrick Troughton and the delightful shenanigans The Third and Second Doctors get into while dealing with the Omega threat. Their raw chemistry highlights the missed opportunity of William Hartnell working more directly with the both of them, but at least he's able to work in a few memorable quips from his viewscreen perch.
Omega himself is a one-(very loud)-note villain who does nothing but bombasts his way from scene to scene in such a manner that would make Brian Blessed blush. At least the serial does the decency of recognizing this flaw and uses it as his ultimate downfall as everyone escapes the antimatter universe. The only true curiosity of the character was the weird mental battle between The Third Doctor and Omega's dark side of his mind.
There were really only two other good things about the serial. First and foremost, how badly the poor Brigadier handled the very concept of multiple Doctors in one time zone and all of the antimatter nonsense. His complete denial and utter refusal to accept any of it until it was staring him in the face was brilliant and Nicholas Courtney's straight man performance was nothing short of masterful.
The other delight was the gorgeous bulbous, rock, whatever creatures. The costuming designs for them were on point and I kind of hope we get to see a modern take on them, but I'm doubtful.