Meh. If Subnautica could be called overwhelming content and freedom, then this game just leaves you whelmed. Subnautica had a huge map and monsters that actually terrified you and made you remember Jaws. This game is like a Chucky Cheese kiddie downgrade to the first game. It's got a way smaller map, tries to compensate with overland equipment and creatures, fails to do so and just leaves a bad taste in your mouth. The monsters are whatever in this one, the big one is a SHRIMP. Enough said, can't recommend. I mean it's ok on its own, just mediocre compared to the masterpiece of the original. If you play this game, don't play Subnautica first or you're in for big disappointment.

just play subnautica 1 instead

It's more of the same, albeit with slightly rougher edges than its predecessor. If you enjoyed Subnautica, then Below Zero is the equivalent of an expansion pack with a lore-oriented focus; if you didn't like Subnautica, there's nothing here to win you over or change your mind.

Highlights of Below Zero include new base pieces (many of which were backported to Subnautica in subsequent patches), a lot more lore about everything, more above-ground elements and gameplay, and arguably my favorite addition: the SEATRUCK!

The only real downsides are some rougher edges in the world itself, and a smaller overall map to explore compared to its predecessor. From landing to completion, it runs about 60% of Subnautica's if you're planning ahead and minimizing backtracking. The lack of an in-game map also remains problematic, as it necessitates either placing Map/Survey rooms and bases throughout the map (difficult to do when Magnetite is incredibly rare and dangerous to obtain this time around), or by using maps in your web browser instead. Having an "auto-map" sonar module to map as you explore in a vehicle would be a great addition for navigation purposes.

All in all, I'd recommend Below Zero to anyone itching for more Subnautica, having finished the first one already. I wouldn't recommend it as the entry point to the series, though, as it's a direct sequel in narrative and mechanics to the highly-polished original.