Cassette decks. How good can it get?

I have a JVC KD-A5 that is set up in my garage I have friends over for music day we listen to tapes in the garage  they still sound pretty good . Then we go to the party room and listen to lp's . The cassette tapes that I recorded were mostly type II  15 -25 yrs ago they still hold up

I was a huge cassette buyer in the '80's and early '90's.  My main deck was an Onkyo Integra TA-2070 which sounded quite good and recorded well.  It was an expensive deck when new in '84.  Bought a new 2 head Kenwood for $220 in 1989 (about all the money I had as a college kid) which still operates very well.  Not a great deck as compared to all the others mentioned here, but has been a solid workhorse for mobile recording projects and general playback if needed these days.  

Totally agree with @bkeske about the retail production tapes from the golden age of cassettes.  Many of mine sounded very good.

I am a big car audio enthusiast as well and the cassette collection allowed playback at home and in the car.  Remember when the HLTAC head on Alpines came out (vs. the previous SCC head)?  I HAD to have a head unit with that tape head and spent $600 on an Alpine pre amp only pull out head unit in the mid '90's just to have increased SQ in the car...Getting off topic here (my apologies for bringing up car audio), but with A/D/S components and power, it was very high fidelity in the car. 

Well they must be producing tapes because a lot of new music comes out on Tape only!  That is what got me stated on this whole tape thing to begin with.  I have aquired a number of new tapes that usually include a download with them, mostly from BoomKat.  I wonder where they are getting blank tapes to record this stuff on. They are usually a special color or design even.  

Unless one has special recordings on cassette already that cannot be had elsewhere, I would recommend to not  bother with cassette. 
 

I still keep my old Yamaha cassette deck around for occasional use.  If I play a tape it is only once and is digitized and added to my digital music library.   Same with old  vhs hifi recordings I still have which provided superior sound quality with a good player in its day. 

The original poster was asking how good can cassette decks get. To be able to answer this question, one has to have hands-on experience with several (if not ALL) of the top decks that have been restored, -or still operate to factory spec, and that are properly calibrated to the tape being recorded on. Understanding different tape formulations and how Hot a signal each tape can take has to be well-understood, and the blank media must not suffer from dropouts, molding or shedding. If you own a Dragon, or "an old yamaha deck" or a "BX300 that is not working", I don’t think you can provide a valid input to this question, let alone recommend or conclude whether to "bother or not to bother with the format". Also, repeating that "the 1000zxl is the ultimate deck" (most likely without owning one) is just not enough (-or true).

Both the Dragon and the 1000ZXL are boring sounding decks with dynamics, scale and slam simply gone out the window. They make lifeless and small-scale sounding recordings, but to their credit, they’re fairly good playback decks (whenever they’re up and running instead of being serviced). Nakamichi themselves chose the ZX-9 for their studios and master recordings, classifying it as their highest performing model. The ZX9 is great (and outperforms a Dragon or a 1000), but to my ears the CR-7 and a 682 are even better. Especially if you record on a CR-7a, and play it back on a 682. But that’s only the Nakamichi brand.

Anyway, in short: the very best sound quality that was ever possible with the cassette format (to my ears), was provided by the Tandberg 911 and 3014 (whenever they were not being serviced but actually worked), the Studer A721, the Technics 9900, and the NAD 6300. These walk all over anything Nakamichi made, these can make the recording sound superior to the source, they are utterly musical, bold, clean, dynamic and engaging.

Record with an NAD 6300 and play it back on a Tandberg - and you will find that the sound quality is now in the territory of a 1/4" Nagra reel recorder.

So to answer the original question: in my opinion, cassette can get very, VERY Good......

From my arsenal of over 100 decks (over the years), I’ve only kept the Technics 9900, the Studer A721, a CR-7a, and two NAD 6300’s. They still serve up immense fun.