naval and amphibious combat looks to be outstanding
https://www.taleworlds.com/en/Games/VikingConquest
http://store.steampowered.com/app/321300/
Bought this yesterday on sale. Only 4 euro's or something. I'm loving it. Heard a lot of bad stuff about it at first, but then they released the 'Reforged Edition (like 2.0)' and it's brilliant. Epic shaders, improved animations and loading, great units. I wish they'd release a source for this so mods can take a peek inside.
I asked about the source and they said they are still stipulating usage permissions.