Subnautica: Below Zero is a submersiver experience
All in all, if you enjoyed Subnautica, then you're most likely going to enjoy Subnautica: Below Zero as well. I would recommend it.
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Subnautica: Below Zero is quite the game. I enjoyed the story of the game a lot as it seemed to have a lot more to it, compared to the first game, plus the tie-in to the first game was a nice bonus. Although, you could the gameplay is a carbon copy of the first game, as I noticed myself barely using any of the new features they put into Subnautica: Below Zero. The biggest drawback for me were the vehicles in Subnautica: Below Zero as they're a lot less fun to use, as the Sea Truck is slow, making every trip in the sea a chore, and the Snow Fox can only be used on the land, and surprisingly, you're not up there that often (not counting the Prawn Suit as it's the first game).