I've gone, and I love it. I would go every year if I could. The way things have been going with the caribou herds as of recent, and with the constant opening and closing of seasons, I would not put it off if you have the opportunity. They closed the season in Labrador last year, and I have not heard if it will be open again anytime soon.
Anyway, as far as the quarry goes, caribou are exceptionally beautiful in real life, where they live naturaly. Their beauty is almost unsurpassed in my opinion. However, as beautiful as they are...they are not whitetails. They are fairly easy to stalk. Easier than wild hogs in my opinion. The biggest thing as was mentioned before is that they rarely stop moving, and they move much faster than what they appear. You have to try to get in front of them...WAY in front of them, as you will not catch up to them. Even on tundra, there are terrian features that will dictate movement to some extent. Look ahead of where they are going and try to find something that may funnel them to bow range.
As far as shooting them goes, caribou are not very tough in my opinion. Try to shoot them just like you would a whitetail. But it seems like if you hit them between the front legs and the back legs they go down. Im jeleous!