My most-played game on Steam with over 1000 hours, and there's still a lot of stuff I haven't done in it. That's without any mods even. I would say vanilla Terraria is on-par with modded Minecraft and I've never felt the need to mod it. Cheap base price, goes on sale frequently, and the devs have supported it for over a decade, just updating the game, not making paid DLC or sequels. It's basically the gold standard for video games for me. Multiplayer is a blast, but the singleplayer can be very satisfying as well. I spent most of my hours doing multiplayer runs with various combinations of friends, but when I last played the game I did my first full singleplayer run and it was amazing. I didn't have to share loot with anyone, I felt more skilled for beating bosses by myself, and the extra challenge got me to research strategies a lot more.
I would say there are two things worth warning people about. One, this is definitely a "wiki game". You will want to reference the wiki regularly while playing. Some people are really bothered by this, so worth mentioning up-front. The other thing I would say is that the game might not click with you right away. There is a ton of progression in Terraria and it alters the feel of the game dramatically. When you first spawn in with your slow tools and limited movement, it might not feel that fun. One of the turning points for me when I first played was getting a grappling hook. No more ugly dirt pillars everywhere, no more dying to fall damage (if you're quick to grapple), you can explore caves from the ceiling and skip past enemies, you can make taller houses/bases and still navigate them, you can get around way faster. It's huge. There are other movement upgrades like a double jump, rocket boots, wings, mounts, and so on, but I think the grappling hook is really the most important.
On my last singleplayer run I decided to get every achievement. Achievements weren't even a thing most of my hours I owned the game, so a lot of them were easy to get from just playing the game, but several I had to go out of my way to get. The fishing quest achievement is bullshit and takes way too long, but aside from that they were pretty fun to get. I also found it weirdly entertaining to collect all the types of glowing moss and create farms for it at the end of my run. It's awesome that there's always stuff to do. You can speedrun the game or you can live inside it doing all sorts of things for as long as you want. Each run can be very different depending on what weapons drop for you or which class you play as. One of the greatest games of all time for sure.
I would say there are two things worth warning people about. One, this is definitely a "wiki game". You will want to reference the wiki regularly while playing. Some people are really bothered by this, so worth mentioning up-front. The other thing I would say is that the game might not click with you right away. There is a ton of progression in Terraria and it alters the feel of the game dramatically. When you first spawn in with your slow tools and limited movement, it might not feel that fun. One of the turning points for me when I first played was getting a grappling hook. No more ugly dirt pillars everywhere, no more dying to fall damage (if you're quick to grapple), you can explore caves from the ceiling and skip past enemies, you can make taller houses/bases and still navigate them, you can get around way faster. It's huge. There are other movement upgrades like a double jump, rocket boots, wings, mounts, and so on, but I think the grappling hook is really the most important.
On my last singleplayer run I decided to get every achievement. Achievements weren't even a thing most of my hours I owned the game, so a lot of them were easy to get from just playing the game, but several I had to go out of my way to get. The fishing quest achievement is bullshit and takes way too long, but aside from that they were pretty fun to get. I also found it weirdly entertaining to collect all the types of glowing moss and create farms for it at the end of my run. It's awesome that there's always stuff to do. You can speedrun the game or you can live inside it doing all sorts of things for as long as you want. Each run can be very different depending on what weapons drop for you or which class you play as. One of the greatest games of all time for sure.