Check it out. A lot of people write it off for factors extraneous to the music itself. Also most people who don't like the record probably listened to it one time 10 years ago while already coming in with preconceived notions.
Musically it's a very unique album. It's very naturalistic sounding record, with melodies that recall nonorganic natural vibrational patterns (i.e. tides, waves, wind). While many artists capture these sounds, they're almost always flavored with distinctly human emotions and sentimentality (the classic example is Beethoven's 6th, but a black metal example would be Drudkh's Autumn Aurora). Save a few moments of the track "Flora and Fauna" Genevieve is totally cold blooded. There's a sense of catharsis, perhaps even a predatory quality to some of the riffs, but no sentimentality, no anger, no sadness, no joy... none of those ordinary human emotions that color 99% of music, black metal or otherwise. It's about as close as you can get to abstracting the human dimension for music while still maintaining melody.
So when people say it's "just nice ambient" they obviously missed the point of the record. It's like criticizing Filosofem for being repetitive or Strength and Anger for being too minimal and raw. Perhaps that's not some people's cup of tea, but I usually try and judge art by first asking: What is this work of art trying to express? and then asking: How well as this work of art expressed what it aimed to express? Judged by that standard Genevieve is a masterwork, because it expresses something that is extremely difficult to express.