Now you got me going back through the Enslaved back catalog and listening to the production on each one to see what I can say about the differences in production. (Not that I know a ton about how to produce a mix, but I have a pretty good ear for listening. In an alternate universe I totally should have gone into sound engineering.) I don't own anything of theirs earlier than Monumension, so that's where I'll start.
Monumension - Very hot recording with all the instruments and vocals recorded so high that the signal is on the edge of breaking up. The recording as a whole is very open and big sounding, but the vocals are behind the guitars and get a bit stepped on as a result. Drums are loose sounding. Guitars are not too compressed, but the signal is so hot that it's clipping and compressing as a result. Big, but raw and angry sounding.
Below the Lights - Dry and compressed overall. It opens up a bit more in the jazzier moments like the flute intro to Queen of Night, but otherwise it is very tight sounding. Drums are tight and compressed. It sounds like a smaller room than Monumension with not a lot of space between the instruments. Not a lot of bottom end to it either. Definitely a more trebly recording. Vocals are behind the guitars again, but not as far behind.
Isa - Warmer and more open again. A hot recording, but not as hot as Monumension. Vocals are given more room in the mix and come through more clearly, but the bass gets buried a lot. There's more bottom end, but less detail to that bottom end as it comes out flat and gets lost in the guitars. Drums are punchy, but the cymbals don't have much detail. Overall a pretty balanced recording, though. Guitars are a bit compressed, but the overall space still makes them sound tight rather than dry.
Ruun - More open again with guitars given distinct space on the left and right. Somewhat compressed, but clear. Drums are articulate and punchy, but dry and compressed. Vocals are a little lower in the mix than they could be, but they get enough room to stand out. Bass is a bit thin and needs more presence to cut through better. As with Isa, the keys really open up the soundspace a lot and add to the sense of dimension.
Vertebrae - Biggest sounding recording since Monumension, but it has a lot more headroom and does not come off too hot and clipped as a result. All the instruments have enough space in the recording to be heard. A bit compressed, still, and Herbrand's vocals lack a bit of presence and could use a touch more reverb.
Axioma Ethica Odini - Lots of space and openness in the recording. Guitars have a decent amount of reverb in the mix to open them up and make them seem warmer. Vocals take a step further forward in the mix and gain presence as a result. Still compressed enough to sound tight, but not so compressed that it sounds buzzy. The vocals sound bigger and better than on any of the previous recordings. If there's a weakness, it's that the cymbals really don't stand out much or have much life.
Riitiir - More compressed again than Axioma, but the combination of the vocals moving forward yet again and the much more open and dynamic drum sound and audible cymbals makes the whole recording seem big. Bass gets more compressed and drops back a notch in the mix again. Vocals have a lot of reverb. Guitars have a bit less reverb. I like Axioma's mix a bit better, but that's mostly a matter of taste and priorities.
In Times - Vocals forward with lots of presence and reverb. Drums are big sounding and have a lot of reverb and a lot of life to the cymbals. Bass sounds round and warm. Guitars have some reverb, but lose some definition so that the rhythm parts are not quite as crisp. First time that the guitars get buried in the mix and stepped on a bit, but only in the bigger, busier parts. Opening of Nauthir Bleeding sounds great. It's only when the full band comes in with distortion and keys that the mix becomes too saturated to provide enough definition. The keys wash out a bit of the guitar riffing. Not a bad mix to my ear, but it does show off the vocals a bit to the detriment of the rhythm guitars. It's like Ivar was being generous to Cato and Herbrand and modest with himself.