How does Rook compare in difficulty to other trick-taking games?
Of all the other card games I know, Rook is most like partnership Whist, with only a few exceptions:


Tournament Rook uses the rook-bird card, which serves as the highest trump card (not a wild card: the rook-bird play still must follow rules of following suit)
Bidding in Tournament Rook is done by point counting, not by trick counting (as with Whist): fives are 5, tens and fourteens are 10, and the rook-bird is 20. (As with Whist, trump is not named until after the bidding has passed out.)
Tournament Rook sets aside a "nest" of five cards on each deal-out that is not used by the players to play the hand, nor are the cards visible. This gives each hand 10 cards. The winning partnership counts the points in their won tricks, plus any tricks in this "nest".


The two aspects of the game I like most (and which make it more interesting than Whist) are the "nest" and the separation of bidding and measure of "successful play" from the number of tricks captured.

There are plenty of other card games that assign point values to cards and both bid and measure success based on those cards (Mü, Skat, Tichu). However, I can't off the top of my head think of other games that also incorporate a kitty of cards taken out of play that get assigned to the winning partnership at the end of play.