Brook, thanks for posting this. Your review means a lot. Like everyone else, I would love to see some before/after shots comparing the M and the MX.
The differences are most obvious in shots done side by side with both M and M/X cameras. As Brook explained, the primary differences are in noise (the most significant difference, IMHO) and in usable dynamic range (also related to noise, which is why I consider the noise improvement the single most significant factor). There were a few scenes done in the "Shameless" pilot that involved night exteriors that were shot with both cameras. That's where the differences are very, very clear. In terms of "making obsolescence obsolete," I would have to say that to a large extent, the M/X is so clearly better than the M that it will ultimately make the original M obsolete for most users. It is indeed difficult to go back to the M full time after using the M/X, something Jimmy quickly discovered.
Disclaimer: I've seen the "Shameless" footage through my connection with Next Element Studios in Burbank, where the show is being posted (as was "Southland"). The footage was observed both using Red's tools (Redcine-X in this case) and a special one-off beta build of Baselight (which will be used for the final finishing). Interestingly (and properly), using the same basic settings in both Redcine-X and the Baselight build produced identical results, as it should.