Actually I enjoyed it too and I'm looking forward to do it in Kiwami but I think that's one of the main obstacle to the road of the 100% for a lot of people.
True that. It took me 5 or so years to get the hang of it (I only practiced when playing Yakuza, and finally got it down on Ishin) but now I'd probably put Koi Koi above it difficulty wise, just for the evil AI (I've lost count of good games gone bad by one seemingly fluky hand!)
Anyway, I'm done with Premium Adventure mode now. Everything has been done toward my 100% target. Awesome fun! And I've now beaten both Amon's. I actually didn't find them as bad this time as my Japanese run, managed to beat them both on hard mode with tactics that actually worked. Here's what I did for anyone interested:
*Keep in mind fully upgraded Kiryu and Majima are basically required, and its a good idea to over level them via their 4th fighting style as well just to make them stronger etc. Also buy up several decent weapons/armor which you should already have access to if you've already done the Dragon and Tiger side stuff for the completion list. Also its a good idea getting used to the different counters your fighting styles have on offer - especially for Majima to make some parts of the Amon fights easier.
Jo Amon:
First phase - the first ton of health bars has Jo using the same Komaki style that Kiryu uses for his Dragon style, I found it best to use Majima's thug style and dodge (which builds heat to level 2) and then dodge behind him and then attack. Basically if you manage to time this perfectly you'll be bashing Amon directly in the back and you'll get a good 4-5 hit square > triangle combo on him. Also keep in mind he carries a concealed dagger on him so you can dodge behind him and do that heat move for extra damage AND if your at full heat bars when you do that heat move you can follow up with a nice strong dagger heat move. Also keep in mind that his aggressive punch combos make for an easy target to use your circle Komaki counter (if you have heat level 3).
When his health drops to the blue heath bars he'll pull out a dagger and start using Majima's fourth fighting style. This is hard if your not careful as he can lay you out difficulty wise. So go into your slugger style which lets you block his attacks AND build heat to level 3. Now you can also use his block > triangle x2 counter move if you are in the calm state (i.e. have no heat) to build heat fast and deal some nice damage. Now equip a weapon and do a heat move for maximum damage.
I liked using any dagger heat move (make sure you get the strongest dagger you can before you enter this fight) and then pull it out right near Amon and pull off the concealed dagger heat move (pull out the weapon in front of an enemy and press triangle as soon as the prompt appears). This deals lots of damage. Also keep in mind you can do similar moves with staffs and other weapons. Also keep in mind Kali Sticks and Nunchucks have two levels of heat moves. Mix it up for maximum heat damage. As long as your careful he'll go down after a few tries.
So on the other hand is a bit of a twat. His cannon has a move that basically 1 hit KO's you if your not careful, and he just loves you stagger you first. As he's a prick I decided I couldn't bothered to fight fair, so instead I did the following:
Get the golden gun from the shrine and head into the Amon battle. Now use the golden gun to build up heat almost immediately and then use the dragon style combo's to effectively keep Amon in a stun lock. So use any square > triangle > circle combo (such as square x2 > triangle > circle). This requires at least one heat bar, and as long as the triangle hit connects you'll be able to land the circle grab attack that will knock him to the floor. Now you can do a heat move, use the golden gun to build back up heat or just start pulling of a combo as he's rising (he can't block while he's getting up so you can just combo him all over again, and then he's on the ground). Repeat this not giving him a chance to get up if you can.
Now for phase 2 - he has an attack helicopter drop lawn furniture into the arena (which really fucking hurts as its blown about!) while So uses beast style moves so he's got hyper armor - meaning if you attack him he can just smash you out of your combo. Instead of attacking heat on, use the golden gun while waiting for a bottle/jug to be dropped from the helicopter. Amon will run for this, so get it before him. This makes you invincible for a short period of time. Payback time! Use your dragon combo's like in phase one as its still the easiest way to damage him, while grabbing the invincibility items periodically so that you can continue pummeling Amon into the ground. A short while later and he should also be down for the count!
Its easy to hate on both Amons for being dicks, but really I'd be disappointed if they weren't insanely cheap and overpowered, so this was actually a really fun set of fights for me. Really the only annoying Amon fight I've ever played was Shinada's in 5 due to the complete one sided nature of the fight (Shinada is nowhere near strong enough to take on any of the Amon clan!), but that's what Warning Signs are for!