I have completed early access.
My total playtime was about 13 hours, probably because I was used to survival games and didn't focus much on building, with the last 3 hours mostly spent struggling with how to handle the fourth angel anchor. The map size is about 600m x 2000m, with a maximum depth of 500m in the early access version. It seems the game only has 4 Leviathans, only 2 of which are truly dangerous, and neither of these two are as gigantic as the Sea Dragon Leviathan, but they are still very scary. The current out-of-bounds area is very dangerous, and I advise against driving any vehicle there, a Leviathan will kill you almost instantly, and there's no way to get it back.
Overall, the game is quite good with many integrated QOLs. My computer isn't strong, but this game still looks good even at low graphics settings.