I don't have much to say other than it's very Taeyang, and basically the same sound he's been doing since Wedding Dress. Granted, he's gotten a lot less immature as an artist and his music is way more tightened than it was in his Wedding Dress days (he was trying way too hard back then). But this really isn't that unique or special for him. He's still the same dude with the same lyrical attitude toward finding that "perfect girl", and when Park Sandara said all those years ago that he was too immature for her, she wasn't kidding.
Him collabing with JM is whatever to me. I was a bit surprised to see JM doing something music related, cause I thought for sure he was gonna sit on his butt and do nothing but the occasional photoshoot. Even so, this doesn't require much, if any, work for JM so in a way it's not surprising that he was down for it.
Also, before BT5 got super popular, JM's voice was much more similar to Taeyang's in tone. This higher pitch he's singing in, that's not his true voice. If he had used his natural voice instead of the one Hive manufactured for him, it'd be pretty hard to tell him and Taeyang apart.
I seriously believe that the other reason why JM doesn't put out music is because he's high maintenance. He's a controversial and obnoxious person. I don't think he can successfully collaborate with others, or that many artists want to work with him. That solo song he put out last year, it was pretty much the same as the one JK did, because both of them were slapped together with a random artist not many people had heard of, and the songs were marketed as being JM's and JK's, not collabs. Therefore, Hive set up those solo songs. In other words, Taeyang is the first artist in a really, really long time to reach out to JM. Taeyang is a way bigger diva than JM, and out-divas JM by a few thousand points. JM probably knew there was status is going along with this, or, dare I say, they were compatible musically. I just know that there's no way JM could have successfully collaborated with the other three BB members, cause GD and TOP would eat him alive the moment he acts up, and Daesung would fall into the background.
I also want to point out that so many armpits will claim JM works so hard as a musician but... even JN has more writing credits than him, not just on BT5 songs (JM has been credited on a total of 5 BT5 songs to date), but on songs outside of the group. JM works hard as a dancer and athlete, for sure, but as a musician, NOPE. He is 100% in the wrong career and he knows it, which is why he's hardly doing anything.
I see JM and how competitive he is when playing any sport, and see how fast he progressed when he studied dance in high school, and he's naturally drawn to these things. I just don't understand how he ended up as an idol.