As all Germans he is very tasty and melodic. He can also burn when he wants to.
Attitude. Kai Hansen have that "I am gonna tear your head off with my guitar"-attitude and you feel it when he plays. He is one of the guys you never have to fear will get ALD. He bursts onto the scene and give you a package of 110% pure energy.
His songwriting is phenomenal, very consistent. Kai has done the same thing for twenty years now and has yet to make a bad album, though some, of course, has been better than others.
Versatility. What is his strength can also be seen as his weakness. He has made exclusively power-metal music throughout his career and is regarded a god in genre, but remains somewhat unknown to the rest of the meal-community. We will probably never find out if he is capable of anything more. The only thing I have seen or heard are some unplugged clips from Japan.
May not be his own fault, but Kai is mostly known for music released over twenty years ago. To this day, Gamma Ray is known as the new band of Kai Hansen of Helloween.
Fast 16th notes are what you notice first when you hear Kai. His rhythm-guitar playing are based on power-chords played in 16th notes accompanied by super-fast drumming.
Kai is a master of writing harmonised guitar parts. Both in Helloween and Gamma Ray harmonised guitar-parts was/is a trademark. It is not unusual that the solos ends this way. Harmonised intros are another favourite of his.
Soloing wise he is very melodic. His solos always have purpose and fits the song very well. Kai likes to build up the solos to a crescendo where he just fires off in full speed. Often with great results.
Hansen has played a red/pink Randy Rhoads-styled guitar since the first Keeper-album. First it was a Rockinger but nowadays he is endorsed by ESP. Live (beside his RR-guitar) he plays two ESPs that look like classic Gibson Flying Vs.
He uses active EMG pups of different types. At this point I think he has 81 in both neck and bridge positions.
He claims that his favourite amp is a Marshall JMP-1 and keeps the effects simple Just some delay, reverb and a wah. And that is pretty much what you get with Kai.
Kai is the godfather of power-metal. The only type of melodic metal that still had some life in the 90s. Helloween that started as a thrash outfit in the 80s evolved into one of the semi-big metal acts in the late 80s when they got the super-vocalist Micheal Kiske and crashlanded after Hansen's departure. Helloween still hasn't bested anything they did on their first three records.
In Gamma Ray he continued what he left behind in Helloween and has been the lead vocalist again since 1995 when Ralf Scheepers left for Primal Fear (after being among the final three finalists to replace Halford in Judas Priest).