OK, I'll list some older ones, that I can highly recommend (some are older - mainly for the reasons that I had much more time playing adventure games these days):

Games by Funcom (from Norway)

- The Longest Journey

Of all adventures that I've played I consider this as my absolute favorite. I won't spoil the story here. Unluckily it's rather difficult to get to run properly on modern computers. :-(

- Dreamfall: The Longest Journey

The sequel to The Longest Journey. I didn't like it so much, mainly because of the action elements. I'd like to mention that in November 2014 the sequel to Dreamfall called "Dreamfall Chapters" is to be released. This game was funded by a Kickstarter. The developers promised to drop the action elements.

Games by Future Games (from Czechia; now bankrupt)

- Black Mirror: Der dunkle Spiegel der Seele (this is the name under which it was published in Germany)

A rather serious, dark adventure. In Germany two sequels were published, about which I can't say anything, since I didn't play them.

- Nibiru: Der Bote der Götter (this is the name under which it was published in Germany)

Haven't played it, but it has its fans.

The next game that Future Games developed (Reprobates: Insel der Verdammten (for this game I also only know its German name)) was rather bad. I really don't recommend it (although the story wasn't as black as it is painted in many reviews).

Games by Péndulo Studios (from Spain)

- Runaway: A Road Adventure

This is probably the adventure game which brought back the renaissance of adventure games. This game is considered as rather hard (small, difficult to find hotspots) and even lead to the concept formation of "Runaway Syndrome" (meaning that you often have to return to "containers" to look whether you find an item in it, for which now a use could be found). Nevertheless: I consider it as a pretty good serious (despite its comic graphics) adventure.

This game has two sequels

- Runaway 2 – The Dream of the Turtle

Here the developers tried to make the game more funny and bright - which fans didn't like (it's still a good game). It is ending in a steep cliffhanger.

- Runaway: A Twist of Fate

In this game the trilogy ends. More dark and serious as the first part. If you play the game you'll notice that the developers wanted to make part 2 "forgotten" since the cliffhanger at the end of "Runaway 2" is resolved completely differently than you would have expected.

Games by House of Tales (from Germany)

- The Moment of Silence

A science fiction adventure that poses lots of questions about surveillance (which is especially interesting if you compare these to the leaks of Snowden).

- Overclocked: A History of Violence (English title)

A dark story about a former American military psychiatrist who has to treat five amnesic teens suddenly appearing with guns. For this he has to go deep into their subject minds. I highly recommend it.

Games by Deck 13 (from Germany)

- The Ankh Trilogy consisting of Ankh, Ankh: Heart of Osiris (Ankh: Herz des Osiris), Ankh: Battle of the Gods (Ankh: Kampf der Götter)

I only played the first two parts of it. The best way to describe these adventure games is: what Monkey Island is to pirate games are the Ankh games to the ancient egypt. The first part is good, but the second one is IMHO even much better.7

Games by Microïds (from France)

- Syberia & Syberia II

A melodrama about a female lawyer who must find the secret heir of an automaton factory who was a genius inventor.