As everyone is likely to have different views on what makes music "good," though some views might be similar, it has to be subjective. It is a "beauty is in the eyes of the beholder" kind of thing. That being said, there are certain objective things that influence subjective opinions on whether a piece of music is good, such as:
1. Melody - is it catchy
2. Prosody
3. Skill and tightness of the performance
4. Quality of the lyrics
5. Quality of the recording (I am not a believer in the opinion that a good song trumps recording and production quality - I think they are almost equally important). When I used to play a new song with a single track guitar and vocal into my cheap old cassette recorder, on playback I would think it was the worst piece of crap I ever heard. However, when the same song is performed with a decent recording, it becomes the second worst thing I ever heard.
6. Dynamics (often overlooked, in my opinion, with respect to a "good" piece of music)
Basically, what makes music "good" is subective, but there are objective elements that influence that subjective opinion. That is my opinion at least.
Dave