Really great deal on the expansion pack. Too bad I caved in to the recent Stellaris Humble Bundle, my first HB purchase since 2016 (lol!). Big mistake! Should have waited for this and the Prime giveaway instead.

sorry but how is this news?

Let's suppose I was interested.
How could I understand what is what? Are all three packs different? Is some included in some other?
What a damn mess.

The Stellaris Wiki has a decentish overview of the DLCs (bottom part under the unsurprising header "Expansion Content") including a feature list, the relevant trailers/release videos and links to the relevant dev posts during development.
As the naming of the packs already suggest, there is no overlap. The wiki uses the same subdivision between full-scale expansions, smaller story packs and sepcies packs.

Alternatively, even the shop here offers the links to the contained DLCs in each bundle on the bundle store page. Especially for the expansions the wiki offers probably more but it's still a reaonable overview.

DLC Packs that cost as much as AAA games, not even indie games. That is some kind of joke...

Thanks!
I wish I didn't need a "roadmap" to understand which pack contains what kind of content, but Paradox will be Paradox, I guess.

WOW, 28-60 bucks for DLCs (even if it contain lot of different new content) - that is not joke, but robbery!

I'd buy all if I'd know that these are all the DLCs and the will be no more new ones. Alas, with Paradox you can be sure there will be new ones.
Ah and Stellaris is not discounted, so no thanks, a big middle finger to Paradox

Indeed.
Also, does anyone know if the extra content from that "Galaxy Edition" is included in any of those DLCs?

It is not - which is a damn shame, because the soundtrack by Andreas Waldetoft is worth it alone.
The current DLC bundles are just the regular single DLC packaged together, the extras from the Galaxy Edition are not available seperately, unfortunately.

EDIT 40 minutes later: Disregard the above. As pointed out by viperfdl below there is an option to upgrade.
Apologies for causing confusion if any, it is not shown in the DLC tab to the right at the store page, but instead if you scroll down and view the entire "series".
Can still wholeheartedly recommend the soundtrack, listen to it frequently while reading and there is a seperate entry even for the complete soundtrack.

No but there is a Galaxy Edition Upgrade Pack.

Ok, I didn't realize there was a DLC to upgrade the edition. So, trying to list everything availble:
- Stellaris: Galaxy Edition Upgrade Pack: Content to upgrade to the highest edition, in case you don't have it.
- Stellaris: Complete Soundtrack: Complete OST, because it seems that's not the one included in the highest edition.
- Stellaris Species Pack: All DLC with extra species.
- Stellaris Stories Pack: All DLC with more stories.
- Stellaris Expansions Pack: All DLC with even more expansions.

Is that it? Not sure if I'm leaving something out.

Yes, together with the two free DLC's mentioned by Lexor this would be the complete package.
The difference between Galaxy Edition's OST and Complete OST is that the complete version included music from all the DLC's as well, not just the main game. 2:41 hours for the Galaxy Edition vs. 5:05 hours for the complete soundtrack.

When selling $150 of DLC is a celebrated thing, these are very sad times.

Will GOG celebrate $500 DLC coming next week?