Really, really good. Especially on the very high quality, I have a Hibiki 21 I bought there last December, that's by far the best whisky I ever tasted (which feels really strange to admit, since I usually drink single malt, and this one is a blend).
Lower quality Japanese whiskys are quite good, but unless you're in Japan they're often quite expensive. Really likes the Yamazaki, found everywhere at low prices there, and quite good overall.
For unusual stuff Amrut was also surprisingly good (Indian whisky), very particular taste. But same thing, will probably be quite expensive outside India.
No, just don't. If you want to add anything the only good thing is room temperature water. Anything colder will only hide the flavor until it gets back to room temp.
Simply adding room temperature water can make the flavors much better though, since it pierces the small oily surface that prevents lots of the flavors from being released, that's especially true on very strong whiskys (almost any over 50% will benefit a lot from this). This can be just a few drops, the goal is not necessarily to dilute it, just to get this reaction (which actually makes the whisky slightly warmer, even if water and whisky are at the exact same temperature, this reaction is slightly exothermic). Any expert taster will dilute whiskys with room temp water to get more detailed aromas, most usually go for around +20% water added, some will often go as far as getting the resulting alcohol level to something around 20%.
Ice should really be added only for the same kind of whisky you'd mix coke or things like that, will make a refreshing drink, but you'll hide most of the flavor, doing so in a good whisky is kind of a waste.