Likes:
2.8 Duramax
Floating D-pillar
Some of the front end styling (although those projectors (?) are old-school - LEDs are superior lighting, and cheap besides)
Interior color scheme (not the controls; I can't improve on how Mooseman described the center stack).
Being an LTZ, I think it needs a little more luxury added, as it will carry a premium compared to the lower trims (unless they somehow come up w/ a 'High Country' trim or some such.) Carrying the two-tone set up to the seats would help a little with that, IMO.
The Dmax badge should've went farther front - on the vertical hood surface would've been good (would remind one of the HD pickups). Also a little smaller, and not as blocky / 'chrome-y' (yes, I know that's a lot of comment about a trim badge, but since they're calling attention to the engine, put the badge closer to where the engine actually is). Can't go on the liftgate; that's busy enough already.
While I like the length of the window in the rear door, I absolutely HATE the 'forward / backward' curvature between the bottom edge of the rear door glass and the side glass / rear quarter (which is also tapered top / bottom; making that area the worst styling elements of the vehicle - bad enough that I'd make a different purchase decision, no matter how good the rest of the vehicle is (e.g.; Pontiac Aztek))
I know I'll be one of the rare people here who like the running boards. They should be color-matched on the LTZ, along with an integrated mud flap - the combination of both stock mud guards & black running boards together - more design conflict. No bueno.
Finally, there's way too much gap between tire & wheel well (something GM has been known for for decades). I see that the wheels are 6-lug - hopefully, they're not a unique offset, like ours are.