Though I’ve seen a few people on the forum mention crashes or minor bugs, my experience so far has been completely smooth and stable. It must be pointed out that as yet there is no ability to manipulate the frequency of material or mob spawns. There is a very noticeable scarcity of many basic materials like gold, flint, and saplings. That is a feature, not a bug. Players who relied heavily on the ability to add extra materials via the world settings in the base game should be prepared for a struggle.
There are new mobs and materials in keeping with the island theme. The three most obvious mob additions on land are parrots, monkeys, and snakes. Parrots are simply the replacement for regular birds. Monkeys are a big nuisance; they will follow the player and attempt to steal any nearby materials. They can be attacked, but they will fling poop in retaliation. Snakes are the most troublesome. They are fairly persistent, and can poison players. They can be found both roaming freely and attack players who cut down trees, bamboo, and thorny bushes.
Most islands are fairly small and poorly stocked, so players will dedicate a significant amount of time to traveling between islands. Several boats can be made right from the beginning and do not require a science machine or prototypes. The boats themselves have health gauges. They last pretty long in most cases, though they can take damage and anybody playing on Willow should be aware that she can cause the boat to spontaneously light the boat on fire like any other flammable item.
There are changes and tweaks thrown in to give players more to figure out. Marine-based foods like seaweed seem to severely deplete sanity when eaten raw. There are tons of new recipes, and existing recipes are different, with several costing noticeably fewer resources. Overall, Shipwrecked does an excellent job at providing new content while retaining the spirit and character of the original game.