The biggest difference between Houdini and everything else, is Houdini is completely non-destructive, unless you explicitly destroy the data yourself. Every other package is pretty much the exact opposite, even Max with it’s ‘stack’. The way that the non-destructive nature of Houdini is leveraged results in workflows that are completely open and adaptable to what ever task you are facing.
TDoro, spend some time on Youtube watching some of the videos already posted in this thread. If you can’t invest some time into doing your own research on the internet, which is incredibly easy these days, you might want to stay away from Houdini. Any way here is a site that focuses on Houdini as it applies to games: http://www.gametutor.com/live/home-live/ The engine stuff isn’t specific to Unity as that functionality is coming to UE4 as well.
DancingPeasant, here are some college level lectures on Houdini starting from the UI and interface paradigms and delving into some pretty deep procedural modeling: Houdini Video Lectures - Procedural Modelling - YouTube