It's a wonderful satire on Poles.
Of course it is. But I think, no - I'm quite sure, that there is much
more in "Pan Tadeusz" than just a satire. Some of the beautiful
old Polish customs are also described there, and I simply love the
impressive descriptions of the nature and wild-life in it.
the book was just one huge joke
It is definately more than just a satire and it's certainly not "just one huge joke".
Also, from linguisitc and poetic point of view, the book is a masterpiece of Polish