Google Cardboard uses much smaller lens than the rift. I've built several mobile vr headsets, with the latest being a modified cardboard. Google's lens are from the durvious dive kit, while I use fov2go lens, which are significantly larger. with the bigger lens, you really feel like you are there. I mean, you can still tell there s a screen, but the 'goggle' effect is pretty much gone. I don't know exactly where the dk2 lies on the subject, but seeing as it has the same screen as my phone, I figure you can expect similar results.
tl/dr: get bigger lenses, I recommend fov2go
