The first synth I bought years ago was a Yamaha DX-21. I didn't do my homework before buying it and I think it sucks. I've never been able to get good sounds out of it.
I said that in another thread....now...an update to this tale.....I recently acquired a CD full of a couple hundred sounds for this synth and it's a completely different beast now! I was shocked at the sounds coming out of my DX after loading the new files in. I wonder why Yamaha didn't bother to program the good stuff from the start? I don't know who made these patches (Kid Nepro?) but lots of them are really good! Some of the stuff still sounds like c**p and the original sounds are on the CD as well. Amazing...I had all but given up on this synth and was seriously considering selling it. I am completely clueless with FM synth programming! Glad I didn't sell it.