i have several thousand hours in SE. The game is very much a Sandbox, think Minecraft in space (with more complex blocks). If you dont enjoy making your own content you will probably find it a bit lackluster.

Though the game has an enormous amount of mods available to fill out anything missing from the base game (my personal recommendations are "scarce resources" and all the "modular encounters" plugins).

I haven't played in a while, but SE always felt like more of a physics sandbox than an actual game. 'Minecraft in Space' is a far comparison. But it's shalow in that there isn't much, if any story, campaign, or real progression to it. It's fun to build in, and has a continued multiplayer fanbase. Worth wishlisting and getting on sale if you like building in Empyrion.

I enjoyed both. my gaming group definitely preferred Empyrion though. especially with the Reforged Eden mod.

I enjoyed building things in space engineers more due to the mechanical aspects. and the fact that you could program and automate things. I enjoyed the hell out of making a giant drill. and the vehicles you can build can do really cool things, check out the steam workshop for cool examples.

on the other hand, in Empyrion you actually get to use the vehicles. and they felt more like my own personalized ship. plus going from picking plants on the surface to launching into space is a great starting game loop. and then once in space you can do mining more easily than space engineers or just take out and scrap opposing ships. or trade is viable.
it can be challenging to get the initial materials required. it can also be unforgiving if you pick a fight above your pay grade, so make sure to save (and prioritize a shield). the building is not as complex, but that actually works for it. my buddy builds some mighty cool ships. I tended to get a cool ship from the workshop and then heavily modify it to make it my own, which is a fun feature.

I haven't played Empyrion since it launched... It was pretty sparse back then.

It's also been a few years since I've played, but Space engineers was pretty neat if you like gathering resources and building stuff. The biggest issue I had with it was the lack of PvE stuff to do. Also in multiplayer, your buildings all felt so fragile. Like stuff would break apart and explode for no reason. It just didn't feel very solid.

Space Engineers is fun. I get addicted to building bases in it.

Just be aware that's an online only game. You can play offline, but they take away mods, your online saves, and every paint texture.