Finally re-installed it (based solely on an Idle Thumbs reference) after not really giving it much of a shot at launch. More accurately, I gave up on it out of frustration. The checkpoints, the seemingly rote health/auto maintenance hooks, etc...
But it all just clicked for me today. 6 hours just fell off the face of the earth, and I'm already fiending to jump back in. I can't explain why - though figuring out the DX10 micro-stuttering bullshit did go a long way.
This may very well end up becoming my 2012 2008 GOTY runner-up behind GTAIV, and that's saying a lot, y'all.