I own Houdini, Oktoberfest, Hot Wheels, and Valhalla. A lot of the experience comes down to settings, settings, settings.
Houdini: I found the factory default settings a bit difficult and was quickly frustrated by the game, and it does include some very tight shots. A BIG HOWEVER though, after making some basic adjustments to all of the settings to much easier requirements, it's a completely different game and went from not being fun to being a blast. I've had many 30 minute games on it so by no means is it "impossible" or "too hard". Settings, settings, settings. Build quality is very good overall, you can tell that API put time into this title. Catapult launches the ball like 20" in the air to the trunk that opens for it. Reverse flippers on straight jacket mode which is mind boggling. The magnets under the playfield add a haunted/ghostly feel as if the machine is being controlled by an unknown force. Very smooth left and right orbit shot. Smooth plastic ramp that is very makable. Also a couple a very tight shots like the Inner Loop or Milkcan Loop. As these shots are notably more difficult due to the narrow width of the lanes, I've seen good pinball players hit these 2 shots over and over again with no issue. So, there you go. If anything, I think it improves your skill by forcing you to calculate where the ball releases off the flipper and improves the player's timing. It has only made me a better as a player, and it will probably do the same for you.
I know I've left things out but these are the main things I felt should be pointed out on Houdini.
It's a quality build, and also sounds great with an aftermarket subwoofer wired into the game.
Beautiful cabinet and playfield too.
Oktoberfest: it has a beautiful playfield packed with interesting artwork and the machine is loaded with ramps and fun things to do. I personally think API invested the most time in designing and building this title. It's just fun.
The huge Corkscrew rollercoaster ramp is a satisfying ramp to climb and lock and has a fun multiball mode. There are 14 tents to try and complete and like I said so so much to do. The opening and closing bar shot is cool. Definitely worth playing one that has been properly set up and adusted. The factory settings are easier than Houdini, but it can be set to even easier, which I'd recommend so you can see more of what the game has to offer. The extra Mag Nab button is alot of fun to control when the ball stops on certain magnets. Quality build like Houdini or even better. Settings, settings, settings!
Hot Wheels: I feel that this game has many pinball basics, a fun theme for the family, and is the best bang for your buck money-wise. I feel that less time may have been put into designing this machine than Houdini or Oktoberfest, which is surprising for licensed theme. Having said that, it shouldn't take anything away from the game, the game is still challenging, has bosses to beat, and offers many other cool car modes like Car Chaos and Loop Crash Multiball where the ball hits into another ball set on a magnet causing the knocker to hit (car crash). And of course, there's Red Line Mania where the whole machine goes dark for 5-10 seconds and comes back on with red lighting and offers a timed multiball with certain shots you can make for high rewards. So, as the game may not seem "super deep", it's got a lot going on and is worth putting time on. Fast flowing game.
Legends of Valhalla: a viking theme all about defeating legendary enemies. Mag-Nab button is fun for using on Thor's hammer. There are 3 metal ramps, and the look like swords which is cool. 3 flipper game which gives it some more depth. It's not overly complicated to play, the shots and design are generally straightforward. The most recent code offers a jukebox option so you can turn the game on when idle and have it play the songs in background. The music was professionally done by "Two Steps From Hell" which is basically a real orchestra. So, it's a nice treat that the game offers, immersive music.
Only 500 of the Deluxe Limited Edition were made, and they include golden powder coated rails, lockbar and legs, real backglass, lighter topper, side art blades, knocker, Shaker. Etc
It's a fun game that you may not commonly see, so make sure to check it out and put some time on it. These titles were designed by Riot Pinball and built by American Pinball which is unique in it's own way.