If you remember the orange push up pops you could get from ice cream trucks or ice cream bin in a store, that's about what it tastes like.
Or orange dreamsicle-ish.
It's super sweet; I can usually devour half a normal pie by myself, but Tang pie has a one slice limit for just about everyone unless you particularly feel like barfing sugary orange stuff later.
People differ on the recipe, but it's wicked easy no matter what ingredients you go with.
It's basically Tang drink mix, cream cheese or sour cream (just depends on your preference and price range), a can of sweetened condensed milk, and you can add/top with whipped cream if you're a whipped cream loving kind of person.
Mix it all together, stick it in a pie crust (you can make your own crust if you're feeling like baking, but store bought is just as good, and any kind of crust will do, though a lot of people suggest a graham cracker crust), shove in the fridge for a bit, and ta-da, Tang Pie!
My fiancee's mom and dad made one a few years ago for Thanksgiving since I had never had it before.
It was lovely, and one pie was good for a whole table of people, haha.