Got a small number of hours in it, 3,200 as I forgot how much the base game was, as I bought it years ago, let's assume £30. It gives me about 100 or so hours per £ spent which is insane value for money in the modern gaming sense.
It's absolutely worth it in my opinion. They have reworked multiple major systems in the game for QOL improvements (but most of those changes do not require the DLC). The progression has been reworked to fit in with the completely overhauled late game that revolves around traveling to different planets and managing logistics between them. So you're not just getting bonus content.
I'm just dipping my toes into the new content but I think they did a phenomenal job of expanding on the base game without just adding another layer of complexity. I won't go into detail in case you hate spoilers, but when I got to my first planet it was a similar feeling to the first time I played Factorio. It brought back that feeling of winging it and having to work out the best way to solve problems, which I hadn't felt since my first couple playthroughs of the base game.
don't know why nobody stated this but space age is basically five times larger than the base game. they've announced that even though the game is coming to switch, space age is not since it has much higher requirements.
me and three friends have been spending on average 80 hours each on a space age game together since the expansion released, and we're currently in the process of getting the third planet (out of five) to produce evenly without getting stuck.
each planet has basically it's own tech tree, and you need to re-learn how to build a factory every time because the conditions are so different.
where we are now, the only resource is "scrap". building a factory here involves basically running the entire process to build something in reverse, disassembling broken machine parts to extract the components, sorting them, and reusing them in new things. we're completely swamped in blue circuits, batteries and low density structures, which isn't much help when you need pipes.
I guess I'm the only person that just can't get into the gameplay loop of building things to make things that allow you to build more things to make things...etc.
If the concept is appealing to you it could also mean that Factorio itself doesn't suit you. For example I find the concept appealing and I did put a fair bit of time into Factorio, but in the end it just didn't click. But I loved playing through Satisfactory and I'm currently playing through Techtonica which I'm also enjoying. Maybe one day I'll learn to love Factorio but in the mean time there are other factory builders that I'm enjoying.
I play for the alien carnage. My factory grows so more xenos may die. If it didn't have the aliens, I would probably get bored, too. Right around the time you need the 3rd tier research packs, it gets slow as shit with nothing else going on.