I'm sure that others will chip in, but I'll give my brief view:
I've several synths and many effects units, but the Rev2 is actually (and surprisingly) one of the few instruments that I rarely send through my external effects loops... The Rev2's effects ARE limited, but they complement its extensive analogue sound-sculpting abilities nicely, and they don't (for the most part) colour the sound dramatically. With the Rev2, I often find myself starting a patch with effects in mind, but by the end of my sound design, the internal effects are either plenty sufficient or left off entirely. I find quite a lot of utility in stacking the same (or similar) patch in Layer A and B and just changing effects or envelope release times, using the two layers to form a single "supersynth".
To my ears, the reverb is the weakest link in the effects section (lacking character or flexibility), but I still find it useful for subtle reverb effects; really I see the power in the internal effects as coming from their ability to be modulated like any other part of the Rev2's sound path, allowing the simple effects to be tuned to the analogue sound nicely, and to become part of the movement in the patch.
That said, the Rev2 does sound particularly special through Source Audio Ventris reverb and Meris Polymoon...