i have a DX-21 and have learned to love it. The manual isn't quite as good as other Yamaha boards I have dealt with, but it's still better than many.
It feels nice to play, but can be a pain to learn if you don't have prior knowledge about FM synthesis. On that subject, immersion alone can help you. It just clicked with me one day while screwing around with it.
I don't prefer the chorus effect, as I think it's a tad noisy and doesn't do enough to emphasize the sounds.
I never liked boards that were a menu slog, the main reason I don't play my Micron anymore, however this board does not rub me the wrong way. It can be a bit annoying when you are trying to remember everything you want to do with the sound, then having to remember how to work the functions.
The pitch and mod wheels feel very nice, especially the pitch.
The overall sound is something I've learned to love. It's hard to describe, but when I fire that thing up, the funk just seems to come out. Also, I tend to get a little experimental and make some odd sounds as well.
I also managed to make a convincing B3 sound on it, so what does that tell you?
As far as build? I can't think how I COULD break this IF I WANTED TO. It's built like a f**k tank!
My advice: go for it.
MU Modular (Moog, Dotcom, STG, Analog Systems, and Moon modules), MS20 (x2), Microbrute, Electribes (EA-1, EMX), microKorg, AN1x, Nord Lead 2x, Blofeld, Alpha Juno 2, DX7, JX8P, Poly 61 (x2), Split 8, TR-505, Monotron Delay, Ace Tone FR-3, Paia Fatman