It's quite nice. Its a bit smoother, less roasty and bitter than FES. I'd prefer FES but they are both good stouts. Of course, Special Export is a lot cheaper in Belgium.
But have you tasted FES and SES blind beside each other? I'm not having a go, btw, I'm just curious. I've never noticed the butterscotch thing. Why is that difference there?
I can taste the difference between the two in a blind test alright. FES has higher diacetyl levels. In all other Guinness beers the diacetyl levels are kept to a minimum. The diacetyl in combo with the malt taste gives what many tasters describe as butterscotch.