The original patches that came on the DX-7 ROM cards weren't at all inspiring but over the years some great patches were developed that were much improved and help establish the DX-7 as a classic.

The keyboard responsiveness of many FM sounds is still hard to find in many modern keyboards. The DX-7 had some great pluk and synth brass sounds. And later versions of FM (AFM) in the SY-77 and SY-99 provided even more programming features plus onboard effects which of course weren't available when the DX-7 was designed. Effects really make a big difference to FM sounds. It can often be very revealing when you switch the effects off on sample playback synths and hear how raw some of the samples actually are.

Like any era of synthesis each technology has its own characteristic sound quality and the DX-7 was the first digital synth to be mass marketed so will always have a legendary status.

Besides if you can pick up a DX-7 or TX-7 dirt cheap it makes a great addition to your studio sound arsenal. And there are plenty of sounds freely available online for it. I still use a Yamaha SY-77 and TX-802.