I love the parts of the Silmarillion describing his "voice in the water" or the other ways how he communicates with the eruchín... and he is nearly the only of the Valar who really helps them in the later days of middleearth 🙁
Manwe is just sitting on his throne and enjoying his lordship. OH, yah, and he drowns Númenor "with assent from eru"... bet he invented that
I think Manwe was the least favorite character for Tolkien to actually flesh out...whereas everyone else you almost feel their personality, especially Melkor and Osse to an extant that he was quick to anger and all that...And Tulkas' love for fighting and laughing.
I didn't get much out of Manwe's character except that he consulted with Eru on certain things, and that he'd permit Mandos to speak, Manwe being powerful next to Melkor was the least of my favorite characters.