Oculus Rift released its second generation dev kit (hence its name, DK2) a few months ago, and as it turns out, it looks pretty cool with the official (but still in Beta) Second Life viewer compatible with the Rift -- watch:
The video is by SLer Phobos Jamberoo, who's shot a lot of SL/DK2 test videos, and, he says, the results are pretty great:
Having never had the opportunity to use the DK1, I can't speak to the difference. However, as a long time SL resident, I can say that the level of immersion and presence is unprecedented. The sense of scale and realism is levels of magnitude above viewing SL on my 27" monitor. For the first time, my brain really believes I am in a virtual world.
Which isn't to say the experience is perfect: