Some short remarks about the above:
PAN-THY-MONIUM: despite the gimmicky aura (saxophones, random timings, and general weirdness) some of the material is really strong. The best of it is melodically rock-tinged but very convincing heavy Swedish style death metal with the above-mentioned quirky additions. The demo and third album I probably enjoy the most, but I haven't heard a lot of the debut.
OPHTHALAMIA: rock-based "black" doom. Perhaps a hybrid of "classic" doom (the SABBATH vein) with some newer influences. Too predicitable for me.
PYREXIA: as mentioned, nothing mind-blowing but pretty decent "Effigy" apeing on the demo and first album. Avoid the later material which is almost exclusively hardcore.
RISE: the album I have ("Shadows of Ruin") is memorably written American death metal with perhaps a touch of European class. Better than anything you will hear today heh.
DETERIORATE: the first album is very heavy, moderately complex death metal, similar to what you would expect from that time period stylistically but better than average in songwriting and execution.
SWORDMASTER: first EP is a very short, straight-ahead DISSECTION rip-off, while the remaineder is retro-thrash through and through. Avoid completely.
MERCILESS: first album and demos are pounding, merciless (heh) speed/death metal, excellent stuff. The riffing style is quite unique. I haven't heard the second album but believe it to be in a similar vein. By the third ("Unbound") they had simplified and hopped the melodic Swedeath/black trend a bit. Surprisingly though you can hear a natrual progression and it does not sound terribly forced. A catchy listen if anything.
ISENGARD: the material varies from pure folk anthems to dark death metal (the first demo, included on the "Vinterskugge" CD) to DARKTHONE style black metal (but even better in places!) to ambientish pieces. Pure genius; obtain both albums as soon as possible, you will not be disappointed.
DODHEIMSGARD: the first disc is great Norwegian black metal. Unique vocals, style, delivery, andinteresting haunting riffing along with Fenriz's fantastic bass quitar work. I would be cautious about anything later which lapsed first into retro black/thrash ("Monumental Possession") and then pretentious Moonfag style post-black metal industrial tinged garbage.