Mortlach is wonderful in every way though is very variable in independent bottlings (can be great or disappointing). The official bottlings are decent enough, and while a touch expensive, both the official 12 and 16 are worthwhile, though other versions are floating around (at the moment a travel retail 14 has leaked into UK online stores and is currently better value for the vintage than the other two). Reading about its distillation process requires some type of doctorate to understand (attached below).
Edradour can be rough but that is part of the charm, and they have made an admirable commitment to releasing as many versions of their product as possible. Even the 10 and 12 mass-market versions are good, and are both semi-sherried in differing ways (one two barrels combined, the other the same stock matured consecutively in two barrels, iirc), but it's the quirky connoisseur options that I would urge people to look out for if they have the money for a little luxury purchase. They have two decanter-style bottles, one of ex-bourbon casks and one of ex-sherry, and both can blow your socks off in their different ways. They also have a virgin oak, and a different full-sherried offering (oloroso, vs. the unspecified decanter edition, not that oloroso is particularly fancy or anything). The distillery owners are wonderful in their wrongthink of associating cask strength with single cask, usually offering such an unpolished and elemental version of their product would horrify a multinational-owned distillery, where you have to whine and whine until they release even a strong version of something, but not so here. I think even their mass-market 12 (Caledonia), chillfiltered as it is, is still technically single-cask. The absolute mad lads. The flavour is a little less 'elegant' than Mortlach, highly cereal but with a lot of water and time it tempers down. The owners of the distillery also own the independent bottler Signatory, and they have a more affordable (depending on your region) 46% sherried version that is a fantastic entry-point. I can't comment on their cask-finished versions (eg. wine), but then I don't really have much time for those in general. There's also a peated version called Ballechin although while it's decent and often reasonably-priced for a 10 yo, the already rather aggressive house flavour can find itself in unceremonious conflict with the peated element, but if you like it feisty, this is that.
Benromach is another distillery owned by an independent bottler, and also produces a rather uncompromising product. Despite their branding of being some type of classic Speyside malt, they are anything but. The Speyside flavour stands for blandness and uniformity and Benromach's 10 and 15 are elemental, rude, smokey creations - not quite semi-peated in the 50/50 sense, but with a strong element of it). The 10 is one of the best value quality Scotches in the UK at the moment, around £10 less than much of its natural competition, and the 15 packs a punch. There is also a cask strength 10 because it's owned by people who care about flavour. Unsurprisingly the owners (Gordon & MacPhail) also do a good bottling of Mortlach, though at 43%, which they seem to believe is sufficient (which Benromach to be fair, it is).
Even outside of this particular sub-interest, Springbank remains one of the off the beaten path places for Scotch flavour tourists to experience. If you like Talisker, Springbank can offer a similar experience that is at once more powerful but also more complex and refined. Like Talisker it is smoky rather than peaty, but unlike the rather rough and (hot take) under-developed Talisker 10, Springbank's 10 and 15 are given the quality of cask and care over distillation required to reach its full potential at these age points. There is also a cask strength 10 because of course there is. Springbank is run with less of a profit-motivation than most distilleries, which allows it a competitive pricepoint vs. similar quality malts, despite enthusiast demand (special editions or high vintages sell out quite quickly). Where distilleries such as Oban and Lagavulin have become soulless robotic nightmares operated by computers and with increasingly shitty product as skilled knowledge by workers is lost, Springbank has become a bit of a mecca for workers in the industry who give a shit about what they make. They employ a lot of workers, and train new generations of people (which to their credit, other places like Balvenie also do) who make product the hard way, through complete control over the crop being malted through the numerous steps before being distilled, and then uses direct-fired stills (an absolute heresy in modern Scotch production, as the process is not idiot-proof). As with Edradour, they take pride in their product and are keen to make available as many versions as possible. As a result, their standard release of Springbank, which is semi-peated, is accompanied by a release of Hazelburn, which is unpeated and nominally in a lowland style, but tastes complex and ambiguous in the way unpeated Caol Ila or Oban do, which a north highland complexity as well, and Longrow, which is fully peated, although alarmingly the base version has gone from 10 yo to no age statement, a single black-mark against a great distillery. Longrow might push your limits a little even if you're familiar with Islay, as it has a certain juicy/floral flavour that can be offputting compared to the crispness of an Ardbeg or the phenols of Laphroaig. The similarly sometimes offputting flavour of Caol Ila comes closest, though that can be rather dry.
If you're a bourbon drinker and find Scotch (outside of fully-peated numbers) to be a little weak or lacking in mouthfeel, do give some of these distilleries a go. They take the slightly 'off' note that makes Glenlivet what it is, and run with it.
Other options are rather one Glenfarclas which is mostly known as a sherry bomb, but is sadly a little old-school in its presentation (43 rather than 46%, chillfiltered), yet still retains some of these big-in-the-mouth qualities thanks in part to their rare use of direct-fired stills. It used to also be very underpriced for what it is, selling unusually in 1 litre bottles, but they're in the process of normalising (sadly). Jura is potentially another, it's highly sanitised in its official version, but independent bottlings have some room for discovery, although often they are only the sherried or unsherried portions. Craigallechie is another slightly rough malt that derives its flavour from its unusual process of distillation, however it's closer to citric north-Highland malts such as Ord, Tamnavulin, and Balblair, or to tie it back, unsherried Jura. Other outliers which may be able to produce product like this, but only hint towards it (good in their own rights, though) include Ben Nevis (can have a very savoury salty quality a little like Mortlach, though not as full-bodied), Tullibardine, Glen Scotia (an over-performer full of dark fruity flavours, also has a limited edition rum finish with some peat), Kilkerran (a good place to check if you want more of an Islay style), Glenturret (by reputation - I have not tried this one, waiting on the new owners to release a better bottling than current). Ardmore at its absolute peak can apparently do this, but it's unobtainium. Highland Park in independent bottlings can either be just rough, or rough in all the right ways (Cask Orkney is great once it settles down), but at this point the original mandate has been left behind, as it's just a good middling Scotch.