I went to Iceland for my honeymoon in January 04. Needless to say we had an amazing time. I guess some things have changed - for instance it was unbelievably expensive, and I get the impression that has changed somewhat. For the rest…
I think it’s a perfect time to go, but don’t underestimate how incrediby amazingly cold it might be. We did the Golden Circle tour (very very much recommended) but by the end of the afternoon we were all so cold we’d get out of the 4x4 briefly, go ‘oh yeah, glacier, pretty’ and then make a dash for the car again. Beautiful but ohgodit’ssocold…
We also got stuck in the snow drifts a couple of times and seemed to spend a lot of time pumping up tyres and letting air out again (well the tour guide did, I sat in the warm car, obviously). The Golden Circle covers geysers, glaciers, interesting tectonic plate stuff and hot springs/pipes.
We booked to go on a dog sled session, but on the day turned out the girl dog was on heat and apparently it makes the others go crazy - so they bumped us to a snowmobile, which was just the best fun. We drove out of Reykjavik a little way to the mountains, put on several layers of insulating suits (I had on thermals, jeans, jogging bottoms and an insulated outer suit and I was still freezing cold) and then spent an hour zipping around on snowmobiles. My nose ran with the cold, then that froze :D.
We also did one of the night tours chasing the Northern Lights - that was ok, but actually our best view was in the taxi from the airport to the hotel. So, keep your eyes open and don’t assume you’ll see them when you’re expecting. I’d also be careful of assuming you’ll get too far North, either. The impression we got (I may be misremembering) was that we pretty much weren’t going to get far out of Reykjavik, it just wouldn’t be passable. Never tried the hiking, it was cold cold cold and so much snow.
I loved the light - it was close to all day darkness, but I found it was more like perpetual twilight than anything else (obviously full dark for long periods). I got used to it very quickly.
You have to go to the Blue Lagoon - I don’t know what it would be like in the summer, but in winter it’s the most surreal otherworldly place I’ve ever been. The water is warm and lovely, but there’s snow and ice on the rocks around it, and the steam coming off the water is … well, I’m struggling with words, to be honest. It’s an unforgettable experience, I’d do it again like a shot, in fact I often idly plan a day trip from London just to go there again - it’s close to the airport so it ought to be feasible!
We also had dinner in The Pearl, which was lovely, although again at the time outrageously expensive. Other than that, lots of walking and lots of … um… honeymoon stuff - I mean smiling sickeningly at one another and wandering round hand in hand, of course.