Ark Nova is my favorite board game, and since I usually cannot get enough of it, I was naturally drawn to this expansion. I heard great things as it was coming out, so I got my hands on it as soon as possible, and I've got to say, it really is one of the best expansions I have played. If there are flaws in the base game, then an expansion should be able to fix that. With Ark Nova, the biggest flaw is that the deck is just so large, and you can sometimes get screwed by RNG. With Marine Worlds, not only did they add a mechanic to fix this, they added two. First, with every sea animal or similar sponsorship, there is a wave icon that progresses the cards on the display one time. This does happen fairly frequently, so players are able to see a much greater number of cards on the display that they will be able to choose from directly. Also in this expansions is the added "Find" ability. Through a university, or other means, you are able to search through the deck until you find a type of card you want, whether that be an animal type, sponsorship, etc.. This greatly helps increase the number of icons you have for what you need, making supporting conservation projects much easier. Also in this expansion are several new animals (not just sea animals), sponsorships, conservation projects, final scoring cards, and perhaps most excitingly, upgraded action cards. A whole new phase is added to the game where players can draft two upgraded action cards with a wide variety of effects that have a very noticeable impact on strategy. This adds a whole new layer to the game that further adds to the replay-ability. Finally, other adjustments are made to certain final scoring cards, conservation projects, and other scoring aspects that "even-the-playing-field", balancing this incredibly deep-in-content game. Overall, if you like Ark Nova, I would highly recommend this expansion pack. Not only does it fix some of the problems in the base game, but it adds more cards and mechanics that make it even more fun.
