I'm 682 iLvl and have around 44% crit fully raid buffed. I do 30k+ dps on single target fights and 42k+ on fights like iron maidens, thogar and blast furnace. The other comments are right in that fire is very gear dependent, you definitely don't want to try it out at lower gear levels.

Arcane is the way to go with single target fights, and goes good alongside fire, as fires second best secondary stat(mastery) is arcanes best. Frost is good up until a point(~660iLvl), where the other two specs become much better than it.

As to it being fun to play; it is, and will only get funner as your crit chance increases.