The only halfway reasonable legal case I'd be able to make against the Ubisoft DRM would either be from a truth-in-advertising angle, or from a fitness for purpose angle. However, I'm under the impression that system requirements on the games state that a constant internet connection is needed, so there's not much to go on from the advertising angle. And with respect to fitness for purpose there are already strong consumer protections in place in all EU countries (if the DRM prevents you from reasonably playing the game the store you bought it from is required to give you a refund), so it's unlikely that anyone would think more needed to be done when that remedy is already available. Basically, although the Ubisoft DRM sucks there are already remedies in place, it doesn't seem to run afoul of any obvious consumer protection laws, and if you think it does then you need to be armed with a much stronger argument than "I don't like it, so it's got to be illegal in some way."

Guys, you think I am about to slay a dragon, but I am not. Not yet. I am not a very selfconfident person, so it's a real challenge for me just to go to the next office, which is surprisingly near by my home, maybe 5 minutes away.
At any rate, like the famous quote goes "Rome wasn't build in a day", I won't expect sudden success. I just want to visit their advice centre and speak with them about the DRM-issue and not just throwing them a complaint right now. As far as my background knowledge goes, the German office of fair trading is having an extra section for internet and privacy issues, so they would direct me there then. But first things first, just going to the advice center and collect some informations and help how to do it. I might aswel get one of those consumer prorection guides to look up how far privacy protection goes "legally".
The petition thing is also comming into my mind, as stupid as it sounds, the Pirate Party could come in handy. I was planning to join a party sooner or later anyway, and they are surprisingly politically active around my town.

Instead of fighting, Lets help him try to accomplish his task the best way possible. If their are any flaws, point them out and offer suggestions on how to fix it. We don't have anything to lose by supporting him.

Thanks alot for backing me up :D
Like I said, I will just visit the advice center first.
I will tell them about Ubisoft's DRM, it's function with Ubisoft's justification, it's "fails", and my issue with the DRM, meaning mistrust of customer, the high chance of espionage by the Publisher, and the requirement of CONSTANT internet connection of a single player game without an offline-option to constantly prove that the game isn't pirated and thus invading privacy and unfair treatment of customers with weak internet and giving up the customer the right to own the bought product.
I will ask them if it's a infringement of the consumer protection law of each aspect I mentioned.
I will not pledge a complaint, more getting enlightened what possibilites are open for me on a legal base.
Aftwerwards I will post the results here, wage this with your opinions and then start a complaint with looking up the consumer protection law I hopefully will have that by now.
Then I post a translation of the complaint here and ask for productive critic to imrpove the complaint. Afterwards I will do my real part in the office of fair trading. Then I hope I don't fail.
How does my plan sound?

This particular argument will get you precisely nowhere. You might as well complain that Crytek practices unfair treatment of customers with weak graphics cards.
What you should be focusing on regarding the constant internet connection requirement, is the server problems Ubi has had, preventing customers who had constant internet connections from playing the games they paid for.

Alright, this sounds better. But Graphic cards are different to Internet connection:
Cards are replacable, the connection not, it's depended on your region.

I haven't seen the actual packaging, but AC2's product description does state the number of missions and weapons and so forth on numerous retail sites.
Given that you won't have all of that at any one time, it's false advertising. Also, not all of them state the always on requirement. Whether or not that's a fault of the retailers or Ubisoft would depend on how well Ubisoft explained to retailers the need to clarify the DRM.
Nonetheless, if the game is being marketed as having a specific number of missions, weapons etc and the number you actually have at any one time is actually lower then it's false advertising.
You certainly need to do your research. I don't know if anyone outside of Ubisoft has a great understanding of how the DRM works. Maybe you could try asking on sites like Piratebay where people might know exactly what it took to crack it.

I could ask the guy who managed to crack it. What was his name again , Skidow?

I don't know. I don't even know for sure if anyone's got a full and complete cracked version of the game. But there was an incomplete cracked version. So someone must know something.

No, not really Unless you consider all streaming media to be false advertising.
I decide to go rent a movie from an on-demand service. It advertises the movie as 142 minutes. So I can sue for false advertising because I only have something like five or ten minutes of the movie on my box at a time?

Seeing as it's sold as a product and not a service then yes, it's false advertising.
On demand service. The clue is in the name. If I bought a DVD and needed to use an on demand service to watch the ending then I'd feel the product was mis-sold. I don't see why I should feel any differently about a game.
If Ubi.com was marketed as a service and Ubisoft's games where titles in that service like say On Live then no, I wouldn't see a problem.

When going into the advice center the attitude you take will be critical to how productive your visit is. The best way to approach it will be to emphasize that you are by no means an expert in the legal aspects of the matter, thus why you came to them for advice on the matter. People tend to be much more helpful if you defer to their expertise from the start. Don't make any claims about the DRM being an invasion of privacy or unfairly treating the consumer- that's the kind of thing you're there to ask them about. What you should tell them is simply what the DRM actually does, as well as what problems people have experienced with it. It will help if you compile a list of reported issues for reference before you go in (such as this story), and will be even more helpful if you can give examples of how problems have been handled (e.g. if someone asks for a refund due to the problems do they get one or do they more often just get given the runaround). In short, you should basically be saying to them "This is what's going on, this is what is currently being done in response, you're the experts on the legal side of these things, is there are legal issue here that could be pursued?"

I always see it listed as "Videos on Demand" and the like. No emphasis that it is a service.
And since it uses the Ubi service (and they emphasized it as a service), then the "game" you buy in stores is the client for the service.
Just grasping at straws with this.

Or you can just stop buying their products.