Cool, I'll definitely check it out. He's a very talented musician!
Yea, I should check it out I really like his singing in Avantasia and as a guest in Delain, this could be really good just based on what I know.
So I'm in the mood to get into this comment thread and shine a light on maybe more obscure Marco goodness.
Obviously Tarot is the big one, his band before Nightwish. They have several albums with some hits and misses, I find the live DVD Undead Indeed is a good way to get into them.
Northern Kings is another big one - it's a symphonic metal project that reimagines 80's pop and rock songs with four of the best vocalists in Finland. There's only two albums so they're worth listening to in full, but if you're short for time, here's two standout solo Marco tracks:
Don't Stop Believing,
In the Air Tonight.
There's also the project Raskasta Joulua which features the same cast + many more Finnish metal vocalists, they publish an album of heavy metal covers of Finnish Xmas songs about once a year and tour Finland extensively once a year. Here's a little acoustic bit from the four Northern Kings guys:
Heinillä härkien kaukalon. Beware that you'll be falling into a youtube rabbit hole if you like this and want to see more - so many priceless live videos over the years. Marco's voice sounds totally different in Finnish.
Floor and Marco shared a song once before Nightwish, this After Forever track called
Face Your Demons.
The guitarist of Sonata Arctica had a few shred solo albums, and on the last one he put out two hard rock tracks with vocals, Marco features on
Last Breath of LoveNuclear Blast Allstars was a compilation project with loads of NB musicians and some surprisingly decent songwriting. Marco features on this power metal song
Inner Sanctuary.
You've probably heard of Sinergy - Alexi Laiho's heavy metal band. Marco played bass for them and shares lead vocal duties on
Lead Us To War and
Last Escape.
Dreamtale is a cheesy power metal band, they put out one particularly ridiculous album featuring Marco's NK/RJ colleague Jarkko Ahola. Before all that, Marco was a guest on a few of their songs,
Where The Rainbow Ends is my favorite, probably because it's a carbon copy of like... several Stratovarius songs
Metal Archives lists a lot of other credits, mostly backing vocals, these are only a few that I remember really liking over the years (that aren't Avantasia, Ayreon or Delain).