For every game, add a game launcher that automatically connects to your server and updates the game when run! Also add the extras in that launcher!
That would be awesome since then I won't be needing to download a new setup everytime GoG release a new update for the game.
Its recommended that you add some kind of online authentication for updates and extras. If not, pirates will DDOS your server to death, which happened to the game DemiGod.

You do realise GOG, in most cases, do not have access to game source codes so they can't build patches (they most likely hack them like fans do) for them so even with your envisioned launcher you'd be downloading the whole package every time there's update and I'd image people would be quite pissed if they had to download and install 4 GB 'patch' to play a game. What they probably could do is make a program that compares users gog file library (I for one have most my GOG games and extras downloaded and organised on one of my external drives) to what GOG server has and offer option to download updated files or missing files and replace the old ones.

Or having an email notification if an update is available. That would be old style though.

Uh? Why do GoG need game source code? Its the developers of the game that makes patches, not GoG. They pack it and distribute it, like Valve does with Steam.
My idea was not to force people to update. I just want a launcher that automatically checks if an update is available. Then can choose to update or not.
If you played Rainbow Six Vegas or Age of Mythology, you was asked to update if you wanted. I just want a system that helps me to update the game so I don't need to look after patches on the internet with Google.

Actually, unlike other DD services, GOG staff modifies games for compatibility (in many cases neither the original developer nor the source code even exists nowadays), tests every game before release and also provides technical support for games. Also GOG games are generally patched to latest official version so you don't need nor should you try patches on GOG versions of the games as retail patches would restore any DRM/disk checks retail game had.
On ocasion however problems arise with GOG games after release and GOG staff try their best to fix the problems (with or without original devs or source code). And because they don't generally have source code, they can't build patches for games even if they wanted to (patch would basically be all the modified files whereas with source code they could just build patcher program that would modify the game files as needed) so they've chosen to rebuild and re-upload whole installers instead when ever they make update to the games. That unfortunately has the side effect of users having to download the whole game again in order to benefit from the fixes that's why I was talking about 4 GB 'patches' (If game is 4GB in size and it's patched by GOG, you'll need to redownload whole 4GB).
Upcoming Windows 7 support that GOG staff is currently working on means all installers will be updated and we'll need to redownlaod each and every one of them when they get it done (that's some 100 GB in my case or 86 games btw :-p).

Right then. Steam has introduced a new way to pay for stuff. It's called and it works like this: you go down to a convenience shop (in the UK and Ireland, one that has a PayPoint), you tell them that you want a card and hand over �10 or �25 in cash (insert your own currency here). You then go to the web store (e.g. Steam, although apparently Facebook also works if you're into that sort of thing), type in the card number and then the credit on the card is used to pay for your purchases. Essentially, it's a gift card for the internet. Considering that apparently it'll [url=http://www.paysafecard.com/exchange/exchange.php?language=en]convert the currency, automatically, GOG's strict US Dollar only policy shouldn't be a problem.
Considering it's vast availability in Western Europe, I think it's a good idea to follow suit.

A list of features requested in this thread that eventually got added would be cool for the novelty value.

I support this. I am starting to dislike Paypal, and I want some good replacement. Maybe on the anniversary?

Not sure whether this is already available for some products, but ntl:
Rocketdock (or any other dock) icons for bonus material.
This would be a .png icon for the game purchased with a resolution of 128x128 or even better 256x256 pixels.
Artworks and so on are a nice bonus but will hardly ever be used, but dockicons would really be usable.

The developer drop down menu is quite sporadic - not alphabetic which makes finding any publisher difficult. I'd say either list all publishers somewhere easy to locate or reorganize the drop down menu.
Also the "Games catalog" menu at the top, not trying to be picky however but I always search topics going in alphabetical order. Bumping this topic for relevance.

First off, I'd be nice to have an easy place to find the list of developers. It's not easy flipping through a list of forty trying to find one, especially when the list is not in alphabetic order. My first reaction to find anything that seems unspecific is to look alphabetically, it's not easy flipping through an unordered list.

It'd also be nice to have the genres of "Games Catalog" in alphabetic order as well.

Bump, for the newcomers.

I don't know if GOG really cares about this and about the games wishlist; still it's nice to have the features grouped in a single thread, and not spammed as hundreds of threads in the forums. ;)

I'll have to second what Gremmi says: MD5 checksums and update notifications would be nice. Searches don't really work very well. In addition, if I do search for something (say "cover art"), and click on a thread, it proceeds to filter the entire thread too for those words, then I have to disable the search filter, and finally hit the page 1 link... being able to have some options as to how search work on a per user basis would be nice.

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Seems I'm a bit late to the party, but Petrell, what you say about patching is incorrect. It is not at all a black and white situation like you seem to be describing.

Let's take a fictional situation here: Pretend the Duke Nukem 3D source code was never released. GoG has made a fix to Duke Nukem 3D's EXE file, and they want to make a patch. They run a diff comparison of the EXE from the previously released version, and their new one. Let's say it tells them that it has noted three changes:
* The character at 322738 bytes into the file has changed from f to T.
* A block of characters starting at the 323449th byte of the file has changed from gY= to az4
* The character Z has been added at byte number 326773.

All they would then need is a progrem that tells them to do just those changes to a users file (i.e., replacing the character at location 322738 to the new character, which would be T). Of course, it's important to make sure things aren't changed in the wrong files and such, so adding a MD5 check (generating an almost unique "signature" of the file on the users harddrive, and comparing it to the signature of the original EXE that they are expecting) along with a filesize check (to further help ensuring it's the correct file they are patching).

Should it turn out the user has a corrupted or hacked Duke Nukem 3D EXE file so that the patcher can't patch it, it could request the user to supply the patcher with the location of a backup of the installer for the game. Since the installer is essentially the full game in a compressed archive wrapped in an EXE file that can "extract content from itself" (so to speak), the patcher would be able to get a valid Duke Nukem 3D EXE from the installer an patch that.

If all else fails, only then would the user have to redownload the full installer.

Now, in a real life situation, unless the file they changed was over a certain size, it would likely be more efficient to release the modified file along with instructions on where to put it. However, for bigger changes, this would lead to far smaller download sizes for end users when changes are made.

In fact, a patcher (that is, the patcher itself) made by someone with access to a source code would still do pretty much the same as one made by someone that is not in possession of the source code. The only difference here is the ease of making the changes in the first place. Someone with the source code will have it laid out in a way that is generally easier for a human mind to process, and would potentially have comments that help explain subsets of code. One without the source code would still be able to generally make the same changes, but would in most cases have to run it through a disassembler to turn it from machine byte-code to assembly language to make it easier to read (which most will still find harder to read than, say, code in the C language).

So why don't GoG make patches? I can't give you any clear answer to that, but I suspect it relates to end-user experience and technical support needs. It is often easier for a computer-illiterate user to download a game, install it, and have it work like it should straight away, rather then having to worry about patches and such. And if the patch fails to work like it should, then users come streaming to the forums wanting technical support. That may very well end in employees having to spend time to track down errors that in the end turns out to be the cause of users being unable to follow instructions given on how to use it. But this is just theorycrafting, and I'm not part of GoG, so I can't give any proper answer to that.

Another vote here for update notifications. And/or make the game's version visible on it's gog page. Where bug/compatibility tweaks were applied, it would be nice if these details were shared with the users, to let them know.

Some games have many mods and community patches available, and it would be easy for us to see what version one game is and what tweaks have been applied to it (if any). For example, ToEE has caused some confusion among users who wanted to know how's the compatibility with unofficial patches made for that game.

For the love of god, PLEASE update your wishlist GoG team - it's a complete mess

Opt-in public collections.
Opt-in public wishlists.
Gifts by username, not necessarily by email, and public wishlist integration.
A purple forum theme (okay, this one is a joke).