The first wave of DK2 are due to get shipped sometime in July, with the rest of the preorders shipped in August.
DK1 had 1280x720 but the screen was a last minute shoe in so a lot was unused, the DK2 has a 1920x1080 screen that is a better fit for the lenses. The perceived resolution should be 1.5 to 2 times better.
DK1 had pixels organised in an orderly horizontal / vertical grid - which may have made screendoor more obvious. DK2 has a pixel layout that looks a bit more like the old hexagon strategy games, screendoor is there but less noticeable (resolution bump helps here too).
DK1 refreshed at 60hz, DK2 at 75hz. That should help a bit, Abrash reckons 90hz is where i starts coming good.
DK1 used regular LCD displays with quite a lot of lag, DK2 uses an AMOLED with much faster switching time. The smearing should be gone with DK2 when you move our head.
DK2 has a slightly higher FOV due to the optics matching the screen better, it should have 110 degrees.
Finally, DK2 has a bunch of infrared LED's embedded behind translucent plastic and a camera to watch you. This changes the 3DOF tracking (that drifted a lot) to 6DOF that shouldn't drift. (You can now move forwards/backwards, left/right, up/down instead of just looking in a certain direction).
It's going to be much better than the DK1, but still not quite there.
When the consumer rift arrives, i'd expect a bump to 1440p, 90Hz and maybe a FOV bump to 120 degrees. Those 3 things should be enough to trick your brain that you are there.
Driving a 1440p screen at 90hz+ is going to need Thunderbolt 2 adapters. The graphics card guys are going to have to work hard on latency and fillrate. A lot of GPU these days is used on shader effects like DoF that are pointless or worse in VR so there sould be the power to do it. SLI / Xfire needs to get better, small framerate stutters are tolerable in gaming. They will make you physically sick in VR.