I'm a big fan of the Mkii (never played an original Llama) - it's a terrific, characterful overdrive, offering fuzzy-edged, tweedy, complex and I want to say grown-up overdrive tones.
I think what I mean by that is the Llama's the kind of overdrive sits in a dark, smoky corner of the bar with a deep glass of bourbon, exhaling cigar smoke, not saying to much or drawing gratuitous high gain attention to himself, but every now and again dispensing terse yet wise remarks that everyone just gets... Ah, so that's what a good low/med overdrive should sound like.
Sure, it stacks well, takes a TS or RM for leads well, cleans up/dirties up responsively, has rich, darkish mids and an inherently fuzzy voice which can or subtle or cutting. But it can also have abrasive highs into certain rigs - Fender into Fender. The Mkiv 25th Anniversary edition addresses this with a high cut knob, adds more gain, makes the pedal smaller - though not Smalls small which are not much bugger than mini pedals - and finishes it with a lush chromed casing with red and black decals. It keeps all the good stuff from from the Mkii.
I'd place the Llama in the same category as RAT or other fuzztortion type drives, but it's more subtle, keeping more of its character at low gain where it feels at home, ready to respond to a volume knob twist. Other reviewers have remarked that it is much gainier that the Mkii; yes there is a greater range on the Drive knob, but it can still be turned down to more classic Llama levels, so Red can retreat back into his smoky corner and jes' do his sweet thang: Keefy, Mike Campbell, Neil Young, low-wattage fuzzy twang.
(No affiliation with WHE.)