I bought Ladytron's new album, i got FLAC+Cassette.. I have a cassette player in my car, and was looking forward to listening to it there.
I was very dissapointed to find the tape of absolutely horrible (by tape!) quality, it sounded so bad I couldn't use it.. Totally a gimmick. I ended up just recording the flac files onto another, blank tape and they sound just fine (by tape standards, actually, by most standards).
I hope the new-vinyl is not as gimmicky as new-cassette.
The mastering of the newer generation of metal records is usually done for digital, and they don't really re-master anything for the vinyl release. Most new vinyls sound OK, but in most cases a record released in the late 70's or late 80's will blow a new one straight out of the water.
Many, many vinyls come with digital downloads, though. Personally, I like having a physical media to hold on too. I'm almost too old to hear any actual difference anyway. :D
Cassettes are kind of a unique creature. Dolby invented a lot of technologies that greatly improved the sound quality of cassette tapes. However, my understanding is that none of these technologies are widely used anymore in the consumer market. So anything you buy made after like 2000, be it cassette or player, will have terrible sound quality unless it's designed for studio use.
Is it possible that you used an old, higher-end cassette player to record the blank tape?
I hope the new-vinyl is not as gimmicky as new-cassette.