I have dived in Galapagos, Panama, Jamaica, Mexico (cenotes and ocean), Honduras, and a few others. Silfra is what you dive to not really see fish, plants, or corals. actually all I saw lifeform wise was some alien looking algae. you dive Silfra because of the icy and magnificently clear glacial water. this water was even more clear than cenote water/halocline. in places it was like floating in space or air.
you dive Silfra because of the location - right where north America and Europe have been separating for millennia. it was wonderfully unique, a bit expensive at 500 for one dive, but you pay for the unique!! the guides were wonderful, on the hour drive in and out I learned a lot of local history as well as about the area (and other places to see, things to do, and even some GREAT recommendations on bars and restaurants where you can eat great and mix with fewer tourists) overall it's a once in a lifetime experience and I highly recommend it - as it is in the top 5 or 10 dive sites in the world!!
arctic adventures came in at a much lower price than their competitors and there were only 4 of us on the dive with our two dive masters. simply amazing ratio!