I've recently been getting into this band so excuse me if I get anything wrong. I believe that my favorite song off of this demo would have to be BC/AD. Mike Browning's delivery with the vocal effects in the beginning are great. It gives you almost a psychedelic feeling to the song. After that throughout the song the vocal delivery and guitar work is perfect, it's an amazing amount of gritty as well as clean/polished. The drums in this song just sound like cannons firing, you can't help but to move your whole body while listening to it. I love the shredding ending of this song, again that guitar work is just peak. Early Nocturnus gives me almost a blackened death metal vibe from the vocals/lyrics.
The Entity is the next track which I actually think could use some work. It's pretty catchy but was just corny lyric-wise. Though it was a very short song, barely even noticeable on the demo. Last song on this demo is Unholy Fury and yes it does feel unholy. It's just a 6 minute song of pure hatred and evil. A lot of the drum work is blast beats but it also plays around with the instruments sometimes. The guitars are eerie sounding the whole entire song, like you're in a forest running away from some creature. The bass is pretty light on this song like this whole album, it's not noticeable at all unless you try to look for it.
Nocturnus Demo 87' is a great place to start if you want to get into Nocturnus. It's a look into their earlier work before works like "The Key."