The positives: There was a solid five minute section in the second half of the episode devoted almost exclusively to the budding friendship between Blaine and Sam. Blaine explained exactly what happened when he cheated on Kurt (it was a random Facebook hookup, Blaine regretted it immediately and it only strengthened his feelings for Kurt) and then Darren Criss and Chord Overstreet sang David Bowie’s “Heroes” with all the charisma and conviction one would expect from actors worthy of prominent roles on weekly television.

The Warblers have pretty much outlasted their usefulness as rivals for New Directions, but as a credible dilemma for Blaine – stay at McKinley where he’s constantly reminded of losing Kurt, or make a triumphant return to his old Dalton stomping grounds – it made sense to bring them back. And if we overlook how terrible both Grant Gustin and Nolan Gerard Funk were as the Warblers with speaking roles, Kelly Clarkson’s “Dark Side” was a respectable choice for a throwback to the Warblers glory days.
—  Hitfix recap of 4.07, “Dynamic Duets.” [source]