The only thing other than adc that is differnt (as far as I know) and an improvement in the v3, is metering... the 2 light metering on the v2 sucks.
just, FYI, there are a few other minor differences
(1) no RCA output on the V3, only balanced XLR output and digi-out. The V2 had balanced XLR and unbalanced RCA.
(2) I think there was a small change to one chip in the pre-section. This was made due to availability of parts. I don't remember the exact details, but I do know that it was quite minor, and that the pre-section in the V2 and the V3 are
essentially the same, but not absolutely identical.
(3) the gain structure is slightly different. the V2 trim knobs take away gain. i.e. you set the big knob to +10dB and you then have a continuous range of 0-10dB using the trim knobs. with the V3, the trim knobs add gain, so when you set the big knobs to +10dB, you then have a continuous range of 10-20dB. therefore, the V3 has a minimum gain of +10dB.
these are all minor differences, but I felt like they should be noted. and I agree with Matt, the meters on the V3 are awesome (and, IMO, are only bested by the meters on the ad2k+)