There's no way Discovery can be reguarded as an easy to program option.
Hidden depth perhaps.
Really it sounds like you are cold selling your synth.

Xils-Lab PolyKB II : Very Easy to program and still a lot of depth

Synthix : Rather easy to program ( and even more when the 1.25 update will be out ) and so deep that nobody has still seen the end of it. ( 8 layers )

You should check out SynthMaster. I'm not saying I like it better than Zebra or several other instruments mentioned here, but ...

It's impressively deep. I've gotten to know this instrument just recently and was wow-ed by it's many features.

Plus, it's got an absolutely elegant and intuitive interface. You were asking about a synth that's easy to program? Synthmaster strikes me as a sound designers dream in that regard.

Synth 1.
(That answer became so common - or "default" if you want - that nobody even bothers to write it down anymore )

tone2 gladiator or nexus are great ones.

Even though it doesn't look like a traditional synth, I'd definitely say Fab Filter Twin. Sounds phenomenal , is easy to program imo and can get deep once you figure it's incredible modulation system

DUNE - very easy and very complex. I think there is a CM edition so you can really get a good idea of how you like it.

The CM edition of Zebra 1 also which is really good. Easy to program and reasonably deep.

Ultra Analog is about as easy as it gets, GUI is nice. Lots of sounds to be had although its nowhere near as deep as DUNE or Zebra2 .

DIVA is easy to program, sounds great and is reasonably deep also, If U-he puts in a mod matrix it will go much further.

Tyrell 2.0
http://www.kvraudio.com/forum/viewtopic.php?t=342062&postday s=0&postorder=asc&start=0
With this new skin its great, fairly deep, very easy to program, sounds great and is completely free.

Synthmaster, try it out but I it depends on your programming level and tastes, though its one of the deepest synths I've ever seen.

The Z3ta+2 looks very easy to program, its extremely deep also.

I don't recommend firebird+. It really is not very deep and is very limited. Sounds good though.

I don't recommend Gladiator 2 either because although it sounds good I don't think it fits what you asked for, again try it out if it appeals to you by all means.

Korg Mono/poly is fairly deep and very simple. Sounds great.

Vember audio Surge, I think is really easy yet very deep. If anyone is selling theirs let me know.

Still not 64-bit right? Such a shame, because I agree - really interesting synth. Cool workflow.

I'll give another +1 for Zebra.

These:a lot of hidden depth

I'll plug fabfilter twin 2 as well. You mentioned multi-osc, resonant filters, and modulation. That's exactly what twin 2 is. That plus delay. It doesn't have any other effects or fancy waveshaping stuff. What it does have is beautiful filters, beautiful UI, and more modulation possibilities than I've figured out how to use (seriously)

i had a dream that delivered a revelation to me, a concept to supplant synplant.

unfortunately it was a real idea and not just a silly gimmick, so it would require a huge amount of research and development effort.

a simple synth that has lots of hidden depth? sort of like the simple tale that has lots of hidden depth? so you're looking for a bonsai synthesizer created by a zen master?

sorry, but he hasn't created it yet.

(insert a scene of falling petals from cherry blossoms with you standing alone, your eyes glossed over meeting this revelation, and your destiny.)

Electrax

deep bro

Holy shit what did you have for breakfast?

So whats the concept?
If it really requires r+d, no one will likely steal it.
At least send it to SonicCharge. Maybe itll get them amped on Synplant again.

Even the simplest synths have tons of hidden depth...