These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
"The Dance" was originally recorded by its writer, Tony Arata.
"Friends in Low Places" was recorded by Mark Chesnutt around the same time as Garth's version (though Garth did do the demo, the last one he'd ever have to make). Chesnutt's version was relegated to a B-side, though.
"Two of a Kind, Workin' on a Full House" is another song which was previously a single for one of its writers; Dennis Robbins in this case.
"Shameless" and "To Make You Feel My Love" were both semi-hits for Billy Joel first (and the latter's a Bob Dylan cover).
"Callin' Baton Rouge" was first recorded by The Oak Ridge Boys in 1978 and then a minor hit for New Grass Revival. Garth managed to zig-zag this trope by having New Grass Revival play on his version.
Two of his duets with Trisha were originally recorded by other artists: "Squeeze Me In" by its writer, Delbert McClinton (Lee Roy Parnell also cut it before Garth got to it), and "Love Will Always Win" by Faith Hill.
Subverted with his cover of Aerosmith's "Fever", which he rewrote extensively to make it a song about a rodeo rider. Oh yeah, and the fact that his version of the song barely charted.
Crowning Moment Of Awesome: A good example in "The Dance". That piano solo after his final lyrics (reprising the intro) can still give you goosebumps.