We went to Alaska on the Radiance in July 2005 and absolutely loved the ship. It is a little smaller than some of the newer ships, but my preference is the Radiance over the Explorer. Don't get me wrong, we thoroughly enjoyed the Explorer, but perhaps the intimacy (if you can call a 2300 passenger ship intimate), combined with the itinerary of Alaska made it our highlight ship thus far.
The food was outstanding, the crew was outstanding (although I maintain our cabin steward on the Explorer, Dean, was the best yet), the kids program was excellent, and the entertainment was terrific.
We had a balcony cabin #9584, on the "bubble", (for Alaska, I recommend nothing less than a balcony), that held the four of us comfortably. We were able to see so much from the comfort of our own balcony, including magnificent sunsets (late at night!), whales, bald eagles, and beautiful scenery. We had a "front row" seat when we went to Hubbard Glacier.
I can't recommend the Radiance enough. I think you'd love it.