Battle Isle 2 (1994) by Blue Byte was hugely innovative at the time, had excellent graphics, music and cutscenes, a brilliant story - and yet failed to be commercially successful.
Maybe it was the limited market (developed by a German studio primarily known in Germany) or the lack of marketing power, who knows.
It was the first strategy game to feature 3D combat animations and unit displays using raytracing and vector graphics. It also offered a huge variety of units for air, sea, and ground combat, including 12 experience levels for each unit (greatly affecting battle outcomes).
The whole series is gravely underrated and overlooked, one of my all-time favourites, and yet I wonder if many non-German players have ever even heard of it, let alone played it at all.
I would love to see this one as a remake or being tackled by an indie dev project. If you are out there - DM me, not even joking, I'd pay for it.