Been playing X4 at my brother's house after he convinced me to try it again and it does look like enough has changed for the better for me to try it again. However, the reason he thought I would like it is due to the Timelines dlc, which I found to be one of the worst gaming experiences I've ever had.

So I'm wondering if GoG have just the base X4 for sale? Steam have it on it's own, but I don't like steam, I'd prefer to buy it here - I just don't want to spend an extra £10 for Timelines when I know I'll never want to play it again. I'm even considering smashing my head against a wall to try to remove the memory I have of playing it.

Unfortunately GOG does not have anymore the basegame available.
Only 2 bundles which both include Timelines.
On the other hand as at the moment both of those packs are in -50% discount especially Community of Planetes edition would be good choice as it will include all other DLCs too (Split Vandetta, Cradle of Humanity, Tides of Avarice and Kingdom End) and those will bring plenty of extra content for base game.

You are not required to download and install Timelines DLC but if you do it will also bring some content to sandbox side too.

Yep, it is playable.

And I'd recommend the same. I'm not into playing timelines, it is not my cup of tea, but the content (ships) that comes with it may be worth a look. Even if you don't play Timelines, you can start a custom game and enable the story states (Quettanaut or Grandmother) so that you have the ships available.

If you so wish, that is :-)

Ahh yes, Timelines. I really like the idea of smashing my head against the wall to rid my mind of the memory. I finally made it through Timelines and unlocked all of the ships (...and new sectors) but I did not enjoy much of it. Timelines forces the player to do things that you would not do in the sandbox, like pilot a mining ship in a sector that is full of hostiles. (Oh, and a timer as well, hurry up and die!) I would not put a mining ship in a sector like that even with a hired pilot, waste of credits. I did pretty decent on the first sections (graph's ?) but that last one was a bugger, spent hours trying to get one star, gave up, then came back to it after a weeks respite. Anyways, with that behind me, I am really enjoying the ships that you can get and the major updates that Egosoft has added lately. I respect a game company that keeps working on a game, constantly improving it, for years. Most game companies come out with a new game, and most new games never receive the polish that makes them great. That is why X4 and No Mans Sky are my go to games for a couple of years now. As far as the custom games go, I need to figure out how to set one up properly. I went that route twice, to circumvent Timelines and get the ships. In both games the Xenon where practically extinct before 40 hours. Also, the economy was terrible in both attempts, very sparse refineries, and the ones that where there did not buy much ore. I did see a discussion about custom games on YT where they mentioned a setting for how hard the game is, as far as the Xenon's aggression, so I will probably look into another custom (modified) game again someday.It might be fun to just throw a bunch of large ships out there from the start and go on a terror run. In both of my custom games I was trying to emulate something like a young gun game, only awarding myself a Takoba starter ship and unlocking the Timelines stuff. I'm not sure if I would do Timelines again in the future if I lose my game saves. Backing up game saves has never been a thing for me in the past, but now I think I will, just in case.