I was wondering specially why there aren't more free games that complete any series that is already here. For example, why didn't they add Samorost 1 and Railroad Tycoon 1? They are already freeware. I understand they are not directly making any money with it, but it would be nice to at least have the complete series here. Also, it could be used to make more people come here and create an account to try them and see how well gog's system works.

GOG has a strict policy on games that are (elsewhere) free. They decide IF and on what conditions met, to distribute through GOG, a game that is elsewhere free. Also, as someone posted before in a specific game i was wondering about (Serena), as per which their devs revealed that GOG refused it being given here besides Steam (they asked GOG), there must be a certain number of votes from community members for gog to even consider it (40 or so, or so it was posted).

Sucks, but, hard as is, why don't you get those from elsewhere...?

Well that's kind of the point. The rightsholders don't necessarily want to donate their IP to promote a third party store.

Imagine the scenario, some who owns the IP to a game donates this to GOG. From that GOG attracts 100 people because of the freebie, and then buy other games, GOG still profits, the IP holder gets nothing. We live in a world where people cling onto whatever they "own" at the time for dear life and squeeze every possible penny from it.

Funny thing is, people like NES think there are plenty of free games here. :P

There is also the case that the IP owner may want to release the freeware here on a special occasion, like releasing the next part of the saga, or introducing an improved version (call it enhanced, director's cut or whatever).

GOG does also tend to add free games during Autumn, for their celebrations, so they may not want to add the games at other times. I will have to double check the releases, but I think we've only gotten one or two free games during other seasons.