Tennessee whiskey differs from bourbon because it is filtered during production. Jack Daniel's Gentleman Jack Tennessee Whiskey is charcoal filtered twice--once before barrel aging--and once after aging. This is opposed to the original No. 7 Jack Daniels (black label) which is filtered only before aging and not after.
Because of this, Gentleman Jack is smoother than its cheaper cousin. I also think the second filtration takes some of the character out of the whiskey along with some of the curious compounds that are generated from years of sitting on oak. This doesn't make Gentleman Jack bad--just different.
As the name implies, this whiskey is gentler than the more raw and uproarious No. 7 (though No. 7 is still filtered once, so it has a smoother profile than an equivalent bourbon). I personally like some character in my whiskey, so I prefer the No. 7. But if you are looking for something smoother and mellower than No. 7, you might be a Gentleman Jack Tennessee Whiskey drinker.