Rez's original visuals now look unpleasantly jaggy, but at the game's core is an experience whose appeal remains intact. Rez HD is little more than a widescreen, anti-aliased, 5.1 surround-enabled revision of the original, but it's pure bliss. It's amazing what a fresh coat of paint can do for a well-built game.
Actually, I think Conker: Live and Reloaded was an affront to the original. I agree with the rest of your piece, in that the remakes are worthwhile (and for Rez, gave me the opportunity to pick up a title I had missed on the PS2). But Conker had its single-player shortened, and its multiplayer completely replaced (by a half-baked attempt to do something the original was never really made for). Honestly, the multiplayer in the original version is what caused me to go find a copy on eBay a little over a year ago. I still find the Tediz-beach-invasion a massively entertaining multiplayer level to play, and I'd love to see it remade in other contexts (custom TF2 map, anyone?). And the bank heist was a glorious, light-hearted version of what Kane & Lynch attempted, and apparently better than theirs is well.