In my review of the standard 105, I mentioned that I was reviewing this 20yo H2H against it. Again, the first notes are for full strength (in appropriately small sips!).
First vapor: (Hot-) Cinnamon and a drop of cherry.
Nose: Caramel or big butterscotch; some vanilla/milk chocolate, but cinnamon-raisin is more prominent. The fruit is rather more (dried sour-) cherry (compared to the normal 105's pear). More interesting (less mellow) than the normal 105; but a touch hotter and sourer (I would have expected the reverse).
Palate: Toffee/caramel with fruit of sour cherry. Then silky milk chocolate and a hot little ginger kick (more than regular 105). Becoming oily with rich honey flavor. Finally easing into toasted marshmallow.
Finish: Toasted marshmallow and light cinnamon in the back, as the ginger heat dies down. Still with a zesty prickle.
Nose: There are still raisins/toffee/milk-chocolate, but something "big and chunky" opened up here, now...: Thick toasting marshmallows and chocolate. Like a dense Toblerone with raisins and floral cashews. I also notice an interesting hot black pepper added to this.
Palate: Essentially the same: caramel with sour cherry, but nuttier now. The ginger has happily subsided. Be careful with water, though: the milk chocolate and marvelous honey can also subside.
Finish: Quite similar but without the ginger burn: Light marshmallow and cinnamon, now with Brazil nut and nutmeg.
You can see my review for the standard 105 for other comments. Here I will just compare the two. Here are their similarities: (Nose) Caramel/vanilla/milk-chocolate (Palate) Toffee/sour cherry/ginger (Finish) Sweet/oak-spice/ginger
And basically what you get in moving to the 20yo is: (Nose) more sour-cherry/black-pepper (Palate) more nut (and without water, more oily ginger/honey) (Finish) more marshmallow.
I was quite happy with the standard 105 and can't say I appreciate any big improvements in the 20yo. My preference between the two is nearly a toss-up. In any case, the price difference (3x-4x !!!) is incomprehensible.
@Frost, Thanks for the comment, I hope it helps-- that's why I write! I should note that the 20yo was based on a sample (though I'm as thorough as possible with samples, including giving some time for oxidation). And it's worth mentioning that it really depends how you drink it: you would probably notice much more of a difference if you added a substantial amount of water. But probably you are not adding much water anyway, if you are purchasing these high ABVs....