At $600 and a May ship date for the Rift, I'd probably wait for the Vive, which currently looks more promising for full VR. I was hoping for a $200 to $400 launch price for the Rift.
The Gear VR is definitely worth considering if you have a Samsung Galaxy S6/Note 5 variant or don't mind getting one. Google Cardboard is also an option if you want a cheap entry into playing around with VR, though it's going to be more limited and the experience is dependent on the device you have (low DPI screens don't look great in Cardboard). It's also not comfortable for long periods, you can get eyestrain or headaches after a few minutes if you are sensitive.