I bought both games a while ago:
I don't really get the praise for Subnautica? It looks fine, but all I seem to do is wait for radio signals, then go to a location, then return. Inventory management is a chore; I now have about 20 boxes floating outside my pod. I have the ability to build a base, but I literally haven't found anywhere to build one that seems to offer any real advantages over the pod location. Getting food and water is a constant chore; I'm constantly having to search around to find bladder fish to make water bottles. Honestly, I'm enjoying Conan Exiles as a single player game a lot more than Subnautica, and I know they're very different games, but Conan Exiles has terrible reviews. Does Subnautica get any more interesting? Not sure if it's worth continuing with it.
As for The Forest, I haven't played it yet because the plan is to play it co-op with my buddy once we're both done with Conan Exiles. I'm really looking forward to it though!