I adore AP's Houdini! It's a very challenging pin but once you accept that you can enjoy the ride.
When I first encountered it I didn't like it and thought the play-field was poorly designed. The more I played it the more I appreciated the layout for it's challenging shots and that crazy fun orbit! All the stage illusions are clever and well thought out in regard to how you 'perform' them- some are super difficult to set up but I love how they play out. Houdini has some amazing multi•ball action IMO!! The magnets that interact with the ball in the lower play-field can be frustrating and at times it feels like the machine is haunted or has a mind of it's own. I appreciate all the history and trivia that is packed into the game, it really feels like a lot of love and passion went into making it. Least that's what I get from it.
I don't own any pins currently but I would highly consider getting a Houdini -feel it's a very deep game in terms of what you can eventually unlock or discover in it and as challenging as it can be I feel it makes me a better player.