Thanks for a thoughtful, well written review
I did think there would be a decent chance that you would like the album, but I didn't expect this positive of a reaction, so that's great!
I'll attempt to give my thoughts on why this should indeed be classified as melodic death metal and what, in my eyes, makes that sub-genre what it is.
From a compositional and 'music theory' sort of standpoint, there's a lot this has in common with regular 'ol death metal.
1) Heavy reliance on down tuned guitars and palm muted "chugging".
2) Death metal style growled vocals.
3) "Dark" lyrical themes about death and other ominous stuff. Although usually with a more sincere angle and less of an intent to be extreme (although a lot of regular and progressive death metal these days has more thoughtful lyrics than in the early years of the genre).
4) Like regular death metal, riffs are usually tied together and repeated in clusters. Could be something along the lines of; play riff A 4 times, then play riff B 4 times, play riff C 2 times, repeat A and B, but do a variation, then transition and play a new section of the song with new riffs and a similar "chunky" structure. The trick is to make it seem fluid and like a logical progression, but it's really quite simple from a song writing standpoint.
5) Double kick drum patterns and generally powerful sounding, propulsive drumming.
6) Lots of changes of rhythmic patterns.
The tendency to have more lead guitar lines is one of the things that separates "melodeath" from just death metal. On top of that, instead of going for this Schöenbergian atonal feel of regular death metal, melodeath tends to rely more on minor chords, similar to how, say, ballads or "sad" movie scores do. This lends the sub-genre a melancholic feel (especially a band like Be'Lakor, who rides this approach for all it's worth), but if you simply shifted the chords and note-scales around a bit, it would sound a lot like normal, scary sounding death metal.
These are the main things that make melodic death metal/melodeath what it is, I'd say. For the record, I'm not sure why this album is labelled as doom. That's a bit weird.