building is required; you can't get gear upgrades without making a base with a fair number of crafting station items. You also need food, and there again, you need stations to cook it and a plot to farm plants. Decorative/fun building can get very involved and some people have built small cities, others giant castles, and so on. You don't need all that, but if you enjoy it, you can certainly do a ton of things with it. Decoration ... there are some decorations and such, and enough pieces to build things that look good. One enterprising person has a screenie of a computer on a desk, for example.

you can tame / domesticate some animals and they are 'pets' of a sort. The biggest one can be ridden with a saddle.

H&H added a fair number of home decoration and construction items as well as workstation items (cooking). It added a lot of changes to the food system -- now you make dough and bake it in an oven; before you just cranked out bread directly from a stewpot.

This is NOT an MMO and it is not much like an MMO. There are no quests. At the end of the day, making food and building a bigger house and combat are the 3 major components of the game. If you need the game to tell you how to have fun and what to do, this is not for you: it is a building sandbox and light survival game.