A lot of reviews on the DX7 you can find on the web begin with "The DX7 needs no special introduction" or something along that line and then go on with their words of praise or criticism. I wonder if that's really the case - if nothing else, the differences between the first and second generations are so fundamental that they really shouldn't be called the same. As far as the synthesis engine is concerned, the first-gen DX7 certainly marked a true revolution and sounded great, but as a complete instrument, it wasn't until the DX7s, DX7D and DX7FD came along that you could properly integrate it into a modern MIDI setup. The second generation instruments, especially the bitimbral DX7D that wasn't bogged down by floppy drive problems of the FD, were and remain truly magnificent synths that are as relevant today (at least in a hardware-based studio situation) as they were twenty years ago when they were released.
I used to own a DX7s for several years, having sold it only to buy a TX802 expander due to space constraints, and I have little but the highest praise for it. Its fast but firm keyboard with positive spring action was very much to my taste, I absolutely loved the sound, and its MIDI capabilities were astonishingly flexible for the time (its two data sliders even send programmable CC's) - I used it as my main MIDI controller and never found it lacking in any regard. The only service it ever required was to replace some of the membrane buttons which stopped responding due to dust build-up, and its internal construction was so neat that I could disassemble it and take out the PCB myself in order to save on the shop's labour costs. As far as its form factor is concerned, it was still a bit heavy to lug around, especially in a hardcase (the original one was a real killer), but at least it proved to be sturdily built - a couple of times.
A common fallacy about the DX7 is that its sound is a matter of opinion, i.e. either you like it or you don't, simple as that. For a synth that can produce such an amazing variety of sonic textures, I think that's a very conceited thing to say. Obviously, if you're an analogue zealot, you're going to hate it just because it's a DX7 but with the upgraded 24-bit D/A converters and the poly unison/random pitch features, I have a hard time imagining anyone really hating the DX7's sound. Programming it - now that's another thing altogether: I really struggled with that myself and I still can't build a patch in my head like I would with an analogue synth. The only real problem for me is the algorithm arrangement: I can deal with the interface, I can deal with the carrier/modulator envelopes just fine, and the LFO works just like on any other synth, but there's just no way to tell how you should go about making a sound. To be honest, I programmed very few patches from scratch, and I think my time would be better spent just going through the patch banks from the internet looking for the right sound. The impenetrability of the DX7 is thus definitely a problem, but at least nowadays, you can help yourself.
As you can no doubt tell, I love the mark two DX7 - I think it's a brilliant and supremely expressive synth and one of the most well-rounded instruments ever. It's versatile, it's tight, it goes really deep (the sine wave is the perfect sub-oscillator, after all), it's got lots of polyphony that it can put to good use, it cuts through the mix better than anything else, it's a competent MIDI controller with a lovely keyboard, and finally, it's built like a tank and extremely reliable. If I had to choose a desert island synth, there are very few others in the world - and none I could afford - that could jeopardise its number one spot.