one thing people have not addressed is azimuth. No tape will sound it's best on a deck that the tape was not recorded on if you do not adjust the azimuth of the playback head to match the azimuth of the recording deck.
The higher end Nak's have this feature. Most other consumer decks you can adjust the azimuth by turning the screws at the base of the head, but unless you know which screws to turn, this is not advisable. The Cassette Deck 1, CR7a, ZX7, ZX9, Dragon, 1000ZXL have adjustable or automatic azimuth adjustment. I've not seen any other brand of deck that has this user adjustable feature.
The higher end Nak's have this feature. Most other consumer decks you can adjust the azimuth by turning the screws at the base of the head, but unless you know which screws to turn, this is not advisable. The Cassette Deck 1, CR7a, ZX7, ZX9, Dragon, 1000ZXL have adjustable or automatic azimuth adjustment. I've not seen any other brand of deck that has this user adjustable feature.