At long last, I have picked up Onder's CD from the post office, and I just finished my second listen of it. I wrote most of the following review on my first listen, then made minor adjustments as certain things came to stand out more on the second go. This is the first time I'd heard any of these bands.
A brief guide to my ratings: they're on a 0-10 scale, where a 0 is something I get nothing out of, and a 10 blows me away (though I didn't give anything higher than an 8 in this review). 6 is pretty much the cutoff for something I would willingly listen to on my own, though I might consider a 5. To sum up my ratings for the mix, I gave four 4's, four 5's, and one of each of the following: 1, 3, 6, 7 and 8. Hopefully Onder will find my review reasonably fair. I try to explain my gripes where they exist.
1) Deneb - Time of the Phoenix
Very nice atmosphere, and buildup of tension. The chanting and female choruses lend a very cultish and mystical feel. [6/10]
2) Absurd Conflict - Across the Wasteland
Opens with some Slayer-esque riffs, then an Eastern theme is introduced on the lead guitar. Badass goddamn breakdown around 2:30 - again, reminds me of Slayer. The dissonant ascending chord progressions which follow the breakdown are quite interesting as well. [5/10]
3) Appalling Spawn - Open Arms of Celestial Home
Upon researching the band, I can definitely hear the Lykathea Aflame similarity - which I suspected at first, but wasn't sure if it was just my lack of familiarity with this type of music that led me to what could have been an overly convenient connection. I'd still prefer Lykathea over this, though; this just seems more like "Lykathea-lite" in terms of compositional depth and tightness of execution. [4/10]
4) Spirit of the Forest - Feasting Trees
This song seems to be aiming for catchiness, due to the prominent lead guitar melodies. Unfortunately, I don't think it succeeds. Nice polka-ish beat around 2:20. [3/10]
5) Brocken Moon - Teil IV
Evil fuckin' guitar tone. The 'hooting' vocals are a little weird... but I can cope. This band seems to know how to make black metal rock, which I appreciate. There aren't quite enough riffs here for a seven minute song, but the ones present are quite good - some of them damn good, to be precise. [5/10]
6) Epuration Satanique - Les Legions du Faune
More creeptastically-cool riffs. Strange production style; the drums seem too weak to me, though the guitar is nicely fuzzed-up. Some catchy riffage around 1:30 to 2:15 which actually wouldn't be out of place in a Maiden song... [5/10]
7) Purulence - Sinking into Transparency
Aww yeah... sick rhythms here. This music conveys a sense of agony very poignantly. These guys seem to take many cues from Morbid Angel (even the trippy solos), and I hear in them a lot of what I love about MA. When they get slow, they make you bleed - when they're fast, you're in a twisting vortex of chaos. Great stuff. [8/10]
8) Fluisterwoud - Een Sinister Schouwspel
Ultra-grim, with recording quality from the very pits of Hell, as well as a furious tempo. The mixing is really awkward - I can't seem to find the right volume to play it at. The short ambient passage around 1:30 is really interesting - I could hear some strange things down in those depths of noise. [4/10]
9) Riz Ortolani - Cannibal Holocaust Main Theme
Uhh... yeah. So we have a, uh... country/pop ballad, with some weird-ass warbling synth-choir noise in the foreground. Doesn't really do anything for me outside the novelty factor. [1/10]
10) Descending Darkness - Gevatter Hein
Has a grainy, harsh-as-fuck sound, which is actually very satisfying. Nothing really stands out to me in the song per se, but it maintains a definite evilness throughout it, and never really bores me. [7/10]
11) Contrastic - Radicals
Some weird-ass kinda techno-alternative-metalcore-ish something-or-other. It's amusing, and listenable; I can't say much else for it. [4/10]
12) Pandemia - Majestic Suffering
Reasonably fun, speedy, murderous DM. Nothing really stands out to me. [5/10]
13) Pandemia - Outro
Not much substance here (it's only a minute long, after all), but definitely a heavenly synth sound. They should try their hands at an ambient album

. [4/10]