Depends how much enjoyment you get out of doing things for yourself. There's plenty of monsters to kill, several bosses to defeat, biomes to explore, a decent building system for making structures and bases. I've found it to be pretty fun, and I'm currently in the middle of making another run through the entire game solo.

Mods can also help shake things up, or get rid of little things that you might find annoying (I'm looking at you, no-teleporting-metals-through-portals).