Many, if not most, of the commentaries about 'Colleen' here on iMDB are.... pretty withering... and if we compare it to earlier Warner Bro. Musicals, or to the fabulous cycle of Rogers/Astaire films coming out of RKO, then sure it doesn't compare. But it's still a good show, given the talent level of the cast and the film's obvious imitation of those musical giants Ginger and Fred. Possibly the worst of all is the music itself.
At several points, both Powell and Blondell are obviously laughing out of character at the screenplay, and they are immeasurably better than the film and their roles and the cast they are saddled with. Keeler and Oakie ! Hugh Herbert! Pretty ghastly roster. But they were both contract stars, professionals, and they turned in high quality performances of the material they were given. Powell was very glad this was the last with Keeler.
Powell was becoming increasingly vocal about the fact that he didn't even like to sing (!!?), and Blondell was writing letters to the executives begging to be given scripts that varied even slightly from the last dozen movies she had made, but the simple truth was, Warner Bros. Didn't have anybody else that could perform these roles, and they didn't have much in the way of scripts or screenplays either. So both stars abandoned Warner Bros altogether when their contracts ran out, and moved on to the best performances of their careers.
It's a shame they couldn't have made those kinds of films in the early and mid-30s, when they were at their physical peaks, particularly Blondell. Happily though, neither of them considered their film careers to be anything more than a great paycheck.