I wanna know that too. Currently I'm assuming that it is still missing Achievements since they aren't listed on the store page.

I already have these games for free from EGS.

I'd rather have DRM-free GOG versions.

But the missing Achievements really ticks me off and makes me not wanna buy them on GOG.

With no missing Achievements, then I would have no hesitation with buying them on GOG.

But achievements would require to use GOG Galaxy, which is DRM Client, no?

I don't think it will be so easy, but - let's try! :)

Yes Achievements would require to use GOG Galaxy.

As for whether or not Galaxy is a DRM client: that depends on how it is being applied on a game-by-game basis.

In the situation of adding the missing Achievements to the GOG version of the Batman game(s) that are missing Achievements, that would not be an example of Galaxy functioning as a DRM client.

i bit the bullet and bought the games again, despite already owning them on steam.

It is an all-time low price. I remember buying them on a sale and if I bought them now, I would save $6.

They are also great games so nice to have a DRM-free version for keeps.

Same here. I bought the Batman games when they were released on GOG, despite already owning them on Steam. I did the same with Tomb Raider, Control, and Wolfenstein. I could have saved a good amount of money if I had better impulse control. One of the days I might learn the lesson.

My dilemma is, whether to purchase some of these Batman game titles using the -85% newsletter discount redemption code, or abstain from doing so, given that:

I had previously purchased a Humble Bundle store's game bundle that provided me with Steam keys for nearly all of the same game titles that are included in the -85% newsletter discounts:

Batman: Arkham Asylum - Game of the Year Edition
Batman: Arkham City - Game of the Year Edition
Batman: Arkham Knight Premium Edition (already includes base game, as well as the Season Pass DLC)
Batman: Arkham Origins (base game)
LEGO Batman
LEGO Batman 2 DC Super Heroes

The only Batman title that currently has a -85% newsletter discount on GOG, that I do not have (via the Humble Bundle's Steam keys), is Batman: Arkham Origins - Season Pass DLC.

I have read up on each PCGamingWiki entry for the above games, and from what I can surmise, the only notable differences between the GOG versions and the Steam versions, from the viewpoint of contents and features, would be:

* Arkham Knight GOG version has an Earth-2 Dark Knight skin that isn't included in the Arkham Knight Steam version
* Arkham Knight GOG version does not have Achievements, whereas Arkham Knight Steam version does
* Arkham Origins - Season Pass GOG version already includes the Black Mask Challenge Pack (adds 2 challenger maps), whereas the Arkham Origins - Season Pass Steam version does not (instead, it is separately listed on Steam)

if I missed other notable differences in terms of included/excluded contents and features that others know about, please enlighten me!

... so with that being said, I am still having buyer's hesitation on whether to:

a) spend more money on getting these GOG versions at -85% newsletter discount prices ... or
b) I could just keep the Steam versions that I had already purchased, and wait for a (Steam key-specific) sale on Batman: Arkham Origins - Season Pass DLC

Questions that only you can answer:
Are these differences between the versions so important to you? I mean: important enough to buy the game(s) a second time?
How high are the chances that you plan on playing any of these games ever again?
How high are the chances, that these games won't be available anymore on Steam, at the time when you decide to play them again (IF you decide to play them again)?
These should be the deciding factors, really.

I own games on Steam, that I could rebuy here on GOG.
But I won't.
Simply because:
a) they didn't meet my expectations, and/or
b) I did enjoy them, but I don't plan on playing them ever again (doesn't matter, if they will be available on Steam in the future, or not).

Rebuying such games (here or elsewhere) would be a waste of money.

But again: only you can answer these questions for yourself.

If you are generally ok with using Steam, and you don't fear them going out of business rather sooner than later - wait for the sale on the B: AO Season Pass.
Personally, I doubt that Steam will go the way of the Dodo in the foreseeable future (probably not in my lifetime).
But everyone has their own spin on that.

Thanks for replying, excellent points you made there. I had become accustomed to seeing many GOG newsletters come into my inbox, whose discounted redeem codes didn't provide an attractive enough discount ... until the Batman -85% off discount came along a couple of days ago and got my attention.

After I slept on it, and mulled it over again ... your points made sense to me, I feel that it isn't worth it for me try to re-purchase these Batman games, given that I have most of them already on Steam from an earlier purchase, even with the attractive newsletter discount of 85% off on GOG.

I can be content for the time being, and wait for Steam to eventually put on a discounted sale on Batman Arkham Origins - Season Pass in the future.

Cheers!