It's either the heavy sherry influence or the fact that it has been produced with significantly older stock for some time: this sure seems older than its - already considerable - stated age. 21 going on 25, at least as far as my bottle (ca. 2016) is concerned.
What we have here is a heavy, massive, sweet-and-dry sherry-soaked, oily and woody nose. Chocolate-covered, rum-soaked raisins; bacon-wrapped, roasted figs; aged aceto balsamico; blackberry and/or plum jam; mulled wine, speculoos and christmas spices; assorted nuts. In terms of sherry maturation, this is definitely more on the fruity-and-juicy than on the earthy-and-leathery side. Having said that, there is some leather to be found, along with other aromas that exude the aura of age: musty cellar, dusty attic, shopworn library books... Zero alcohol on the nose despite the elevated ABV, but it's also not exactly easy to locate the distillery character behind this wall of deep and dark sherry aromas. So this is the one quibble I have with this otherwise pretty perfect nose - the PX is perhaps just a tiny bit too prominent. But enough grousing; on to the palate!
Without water, there's an immediately leathery, nutty and (given the unmistakable PX influence on the nose:) surprisingly dry attack, with an incredibly rich and mouth-coating texture. Then the juicy sweetness and the robust Glendronach Highland character hit home. There's a sense of peppery heat, but it's nowhere near as pronounced as in the 18-year-old Allardice. The burn (if you can even call it that) here is much more restrained, and, given the sticky, syrupy aspect of the palate, even welcome. Finally, some bitter notes (black liquorice, black coffee, dark chocolate) join in, along with a faint mintiness. Intense and thick throughout, without ever losing steam.
Finishes strong and substantial, with a warming afterglow, then continues to stick to the insides of the mouth for a good long while, with the typical Oloroso notes of liquorice and leather as the last notes to fade.
Clearly a high-class sherry monster, with the superb Glendronach distillate struggling, but not outright failing to assert itself. What I found most surprising about this one was that the wood was most discernible on the nose. On the palate and in the finish, it almost slipped my attention - either because the sherry overpowered it or because it merged with the sherry so harmoniously (depends on your perspective, I guess).
So yeah: a bit brutal and crass, but also just simply a blast. An event of a whisky.
P.S. Water brings out (even) more umami aromas, adds an intriguing floral element, sweetens the attack, eliminates any burn and reinforces the wood in the finish. Obviously I recommend adding some.