Depends of your tastes. If you want your worlds populated by the dick-shaped monsters every 14-years-old all over the world has ever created, you need the online part.

If you're sane, though, you might survive without this "feature" ^^
In this case, the worlds will be populated by :
- the game's pregenerated creatures (most of them decent looking, and with some variety, although you will probably have some repetitions on subsequent replays)
- your own creations (and it's quite cool to notice the animal you're hunting is one of your old "characters")


As for the game itself : I played it without the expansion, and it was fun making my own chtonian abominations and having them wandering about, but I lost all interest when I got to the "space exploration" part.

So it's nice if you're the creative type and want a casual life-sim. Not great nor challenging, but "mess with pretty stuff for a few hours" fun.

Maybe the endgame got better witn the expansion? Can't say.