Well I tried a gorgeous Amber Sunburst one of these SL4s today and was extremely impressed for the most part. Let's start with the good.
The sound. Normally I find neck-through guitars lack sparkle and snap but this one didn't! Whether this is due to the alder sides or the real Seymour Duncans (I think a TB4 and an SH1n) I don't know or really care, it sounded superb. It blew the RG550EX I tried it against (admittedly the SL4 retails at £300 more than the RG) right out of the water sonically.
Visually it left very little to be desired. Even though it was just a very thin laminated top it exhibited excellent flame and a tasteful and subtle "amber sunburst" very much like the Gary Moore Les Paul. And that's coming from someone who's not into "flame tops" (admittedly I'd have prefered a black back rather than the mid brown stain that was present. EVH's Musicman set the standard on that as far as I'm concerned. Flame top, binding, black back, no arguments.)
The action was slinky and low, just how I like it, with a little but not too much buzz.
Now the bad. The inevitable problems with the Jackson JT580LP (read TRS) bridge that wouldn't play nicely for me, or the very helpful shop guy. At all. It'd need a full set up with screwdrivers and cursing to get it to stay in tune after even slight whammy use.
The other bad thing was the sticky, sticky neck. I don't know if Jackson were using copydex in their lacquer but they might as well have been
and I have no idea how much sanding it'd take to get the goop off the back of that neck.
It was on sale at £659 down about £400 from it's retail price!!! Which made it cheaper than the RG550EX. IF only I could have swapped the neck and trem (and ok if we're honest the overall body shape) from the RG to the Jackson we'd have a winner. As it is I'm gonna go find my RG770 from the guitar cupboard and have a blast. when I've finished reading the forum that is