Difficult to put into words really, I just love how they feel, the necks are superb (a lot more playable than many people would think).
I first played one back in the 80s - the father of a girl I was seeing at the time had an old Gretsch double anniversary & I couldn't believe how nice it was to play, it just felt like it was made for me.
I play guitar with a very clean sound, with lots of reverb & tremolo & Gretsch guitars do the sort of sound I want perfectly, especially with the Bigsby to give the notes a nice wobble. You can get a great rock guitar sound of them them too (most of the guitar on "Who's Next" is a Gretsch 6120 as I'm sure you're aware). They are very versatile guitars, unless you're playing really high gain metal stuff where the hollow body would be a problem.
The Korean models, like the G5420t that you've been looking at, are very good quality guitars. I used to have a Korean made Duojet & that was a superb guitar.