I hated it.
We only ended up using it on a few tracks on "Life, Style". It was hard to program, combining a brand-new synthesis methodology (frequency modulation, a.k.a. FM) with one of the worst user interfaces ever to grace a popular keyboard. At the time, we (like almost everyone else) were unable to move much beyond the presets.
Parenthetically, it also schooled me on the dangers of beverages in the studio - I spilled a bottle of diet Pepsi Free into the key portion a week before a major gig. Ended up costing several hundred dollars to fix and I had to borrow a Korg Poly-800 to cover for it. Ouch.
A few years ago I traded a hot pink Ibanez Steve Vai Jem 777 for a DX-7IIFD, largely because I was interested in exploring alternate tunings, which the IIFD did (and was one of the only keyboards to do so). By then, I had learned enough to understand FM - but the interface still got in the way.
And no matter what, the DX series always felt like work. I never once sat down and said "ooh, this makes me want to write a song!"
The first synth I ever had was a Casio CZ-101 which my parents bought me for Christmas. I loved that thing and could program it 9 ways to Sunday. My brother sold it a few years ago after I asked him to take care of it for me (I guess I should have been more specific about what I meant by "take care of it for me!").
I still have horrible ancient recordings of that thing - seems like I couldn't touch it without starting to write something. Ironically, it was only slightly easier to program than the DX, and far more limited. And definitely not considered "pro".
But given a choice between the two today, I'd grab that CZ-101.