I was there for 5 days. I'm an avid traveller but I think it was my most disappointing trip. It's ridiculously expensive Eur8-10 for a drink, EUR20+ for the most basic main course burger, pizza etc.
I found Rekyijavik (I can't even spell it still ) to be very small. Plus we never found this wild nightlife people talk of. I was 24 when I went. I think I might have appreciated it more if I was older.
All the excursions were very expensive. I think we paid a couple of hundred for a one day trip to see geysers, extinct volcano crator etc. The Blue Lagoon was the best part of the trip for me. Also I'd packed for the North Pole type weather and it was 12c - we saw no snow except for on the mountain tops. We booked with Wallace Travel in Dublin and it was quite reasonable. The hotel included wasn't the best though. I think there was an opportunity to upgrade for more which we should have taken. Taxis were also very expensive. Outside of the tours we didn't find much to do.