Helloween

German Heavy Metal may not be the broadest of categories.
Dominating that list would be The Scorpions, Michael Schenker, Accept, Rammstein and Kreator.
Yes, there are probably many others, but as I don't own anything by them (or have never knowingly heard them), it's a bit difficult for me to comment

Anyway, one more band to add to the list: Helloween.

Formed in 1984, signed to Noise International and released their debut by mid 1985.
'Walls Of Jericho' included the track "Heavy Metal Is The Law" which gives a clue to the content - thumping drums, crunching guitar, volume cranked up - in short, a slab of thrash metal with, if I'm honest, few redeeming features.  It sits well alongside mid-80s thrash outings from Europe, but is not one I'd play again in my later years.

A change of vocalist in 1986 also heralded a change in the bands sound - the Metal they were now producing was closer to the Iron Maiden end of the market.  And in this vein, the and intended to release a double concept type album titled The Keeper Of The Seven Keys.
Lofty thoughts for a relatively low selling band on a relatively small, independent German record label (albeit with a licensing deal with Megaforce International in the US)

As a result, these lofty thoughts were reined in and the record label won out with "we'll release a single album, and if that's successful you can do part 2".

And with that promise ringing in their ears, they honed own the already written songs and sent forth an 8 track album.  The rough thrash edges were smoothed, new vocalist Michael Kiske provided a Dickinson-esque platform, Kai Hansen handles most the guitar work (in the absence of second guitarist and songwriter Michael Weikath), the drums thump, the bass plods, and what is produced is very enjoyable 37 minutes
Bookended by 2 similar pieces ("Initiation" and "Follow The Sign", it comes flying out of the traps with"I'm Alive".  That pace may not be maintained - there are some almost "Metal By Numbers" tracks present, but "Future World" and  the 13 minute multi-movement track (the near eponymously titled "Halloween") keep offer more than enough redemption and return-ability.

And with the critical and public acclaim, the band went on tour for nigh on 2 years.  And in the middle of their world-schlepping, Noise International held good to their word and released 'Keeper Of The Seven Keys Part 2'.

'...Part 2' isn't a bad album, it just doesn't feel as vital or worked at as '... Part 1'.  The fact it was written and recorded during tour down-time, and the increasing tensions in the band, just may explain the shortfall.  The album is dominated by the returning Michael Weikath, which is bound to affect the consistency and flow between the two parts.
By late 1988, MTV was heavily playing "I Want Out" - a single lifted from '.. Part 2' which was effectively Kai Hansen's resignation letter.

1989 started with a new guitarist in tow, and a change of record label - signing with major label EMI, quickly followed by a Breach Of Contract lawsuit from Noise International.  This basically stopped the band touring for the best part of 3 years.
Which should mean that without the distraction and efforts of touring, they could settle into the studio and produce a masterwork.
Sadly not - the resultant album 'Pink Bubbles Go Ape' (1991) shares more DNA with US Hair Metal than early Thrash days or Seven Keys Maiden-isms.  The fan-base was not convinced, and the album barely broke even.
One more album followed before EMI cut it's losses.  And add to that the departure of the vocalist and drummer, they stumbled on with their appeal growing ever more select (but continuing to sell well in Germany, Scandinavia and Japan).  Past members have returned, and they've even managed to update the 7 Keys tale with the album 'Keeper Of The Seven Keys: The Legacy'
(note: I've listened to it twice on Spotify - it's OK, but I'm not sure I'll be investing)

They may not be in the Premier League, but perhaps near regulars in the Championship Play Offs).  In a relatively small pool, they deserve a place in the pantheon of Germanic Heavy Rock merchants

I'm Alive

Halloween

I Want Out