Hi I've used a prophet 08 many times in the past, and always liked the sound but also found it wasn't quite there for me in certain key aspects. Still a very good synth and one of the best modern ones. I just never felt I liked it enough to buy one myself so continued just using a friend's one at his place now and then.
Fast forward to today, I own a REV2 and can say it really is so much more than the sum of its improvements over the Prophet '08. It doesn't negate the Prophet 08 at all , if you are happy with the '08 then you still will be/should be. Afterall new synths don't usurp vintage and often simple synths from the 80s? both are fine.
I do feel however that with REV2, dsi have hit it out of the park, It's absolutely stunning from top to bottom. Design, U.I, Sound extras, Keys and everything to me is above and beyond the Prophet 08. If you are on the fence about 'upgrading' I would definitely go for it, if you won't lose much by selling your '08.
They have improved REV2 so much and added in so many nice and important sound creation abilities, it is like a different synth entirely (but in a good way that Prophet 08 users could still get used to fast). I give the REV2 10/10 on usage and sound quality. I would have given Prophet 08 a 7/10 on both. That's how much better it is to me. The sound moves me more, inspires me more. It opens up the synth, makes it more lively, more "analog", it's closer to what I'd call a real Prophet now, even with DCOs. It does not live in the shadow of the Prophet 6 (or even 5) any more in my eyes. In fact those synths now look rather lacking by comparison (and I don't just mean spec/features)
The REV2 to me is the most exciting new instrument in a long time, which in a large part is exactly due to the new stuff it contains that is missing on the '08, inc the polysequencer, the shape mod, the key feel, the sub osc and the effects engine. The effects are not just thrown in for good measure (like a Prophet 08 with some outboard) they have formed very tight, intrinsic parts of my sound design in ways no external effects every could. That they can be modulated by the ample onboard sources is brilliant and opens up the Rev2 to being able to make a massively wider world of sounds than you could ever do on a Prophet '08 (without some very convoluted and non inspiring hoop jumping involving lots of other gear).
Rev2 is just all there, ready to play, program and inspire. And to me it looks great, even nicer than Prophet 6 (thanks mainly to its correct proportions as a 5 octave keyboard!) but even the new red backlit buttons (the best buttons I've seen on any dsi synth looks wise) the sharp black OLED screen (big improvement over Prophet 08), the layout and even the Font used (yes I for one actually prefer this modern look to "Prophet" vs the old fashioned, if sometimes admired, original font style). I'm very glad they did go ahead and stick "Prophet" on it and changed the name. This synth probably deserves that title more than any other in their range (ok.. Yes the Prophet 6 too). I honestly was never in love with how the prophet 08 looked either, nor the very 90s looking button shape, the sticker panel, the wall wart... it was a great sound source but not something I could really love. Sound is more important of course but to me it also has to look the part and feel the part (solid build) and REV2 is night and day over the Prophet 08 there. The only thing I could have wished for is the Sequential badge in place of DSI but that would be seriously nit-picking. I understand why they leave that for the VCO stuff, that's fine.
It just looks like a modern prophet fit for the future, as a workhorse live and in the studio, I think it'll continue the legacy of its father (the 08) into the next decade and really does sound better. It can get far more organic and vintage sounding by using shape mod, new slop etc. It can sound warmer with sub. And it can do things that many other synths can do that the Prophet 08 couldn't (bandpass and highpass by modulating the hipass effect along with the lowpass where needed).
A creative workhorse that exceeds the original in every way as far as I can see. I honestly don't know any reason to choose the original over REV2 if you have the choice and money wasn't an issue.