Considering that it was made in 1967......
I guess it was good...then. I've seen it a couple of time many years ago.
Watching it again today, I found it laughable in many ways. The "bad guys" going in and out of the apartment so many times, making calls..etc. was so ridiculous and more like a joke compared to plots from movies made in later years. Audrey Hepburns gasps and "oh, noooooooo" when she realized what was happening, was very over-the-top. Not good acting at all. Then there's Suzy finding out that a woman was murdered and dumped close by, and Mike tells her about people looking for the doll, she doesn't lock her door. People just come and go..
This movie would not make it today. More of a bad comedy than a thriller.