Houdini (which I've owned for ~2 years) does have some 'stop and go' aspect to it, but I don't mind that at all. But when you light it up, there is a lot going on which is a blast, quite a rush. Don't worry about the narrow trunk shot that everybody mentions. In my opinion, my GB right ramp and even my BM66 right orbit shot give me much more grief. I can usually hit the narrow trunk shot. Ditto on the Milk Can shot too. I have mine set to 'easy', and in that configuration, it's very forgiving. You do need to think about how to make a shot rather than just blasting a ball around. Wife just got 3.8M last night on the new code.
I noticed you have a ST, and so do I. Houdini doesn't flow like ST (which is pretty darn smooth), but that's one of the reason I wanted Houdini (besides the theme)...I like to have a mix of pins that play different.
Like most modern pins, the code in Houdini does an excellent job of pointing you in the right direction. Build quality is spot on. There was a power supply issue early on (wasn't regulated), so if you do get one - check for the power supply upgrade.
And given the prices I've seen at times...quite a bargain.
Haven't played Avengers (yet). I heard the code is rather deep.