Machinarium is "professional".
There is a certain class of games that just make other games look amateur. "You can play around with your guess at 'fun'," they say with lordly caliber to other games, "but when you are done, the big boys will be over here with the quality." These are the kind of games that define a genre and spawn imitators. These are the kind of games that people will still play after the imitators are gone.
That's not to say that these games are perfect, but they exude so much confidence that we ignore their failings. They rewrite the rules for what a game in their genre has to be. Mario. Half-Life. Final Fantasy. Uncharted. Metal Gear. And, amazingly, sequels as well: Mario 3 and FF4, for example. (Maybe because the team didn't change between games, and they were brilliant TWICE?)
Without these games, a genre stagnates and falls into repetition. Look at JRPGs. For at least a decade, the only innovation there has been the guts to not have a spiky-haired, conflicted protagonist once in a while. Breaking with the mold isn't as exciting when you immediately pick up the previous mold.
Western adventure games lacked confident games for almost a decade too--probably the confidence got worn down during the period when FMV adventures were supposed to be pretended to be good, then later when 3-D graphics were supposed to be pretended to be good (at that time, neither were, but nobody was allowed to say so). In the meantime, the good adventure games were the kind of innovators that boldly went back to non-3-D graphics and proceeded to nail one part of the old formula. Like Longest Journey, which did dialogue really really well. (And really really long.)
Machinarium defines the new standard for western adventure games. All adventure games after this must have a built-in hint system. Little puzzles scattered throughout. Maybe even wordless interaction.
More importantly, the reason that Machinarium is great is that it builds a world skillfully, like a pencil sketch, from a few well-placed lines. Despite the spare characterisation, the world is internally consistent. The game is funny, but lets the humour arise naturally from its whimsical world, not by making constant wisecracks. Every puzzle, even when it is frustratingly hard, is a delight to watch in motion.
Like other great games, the small points of brilliance outweigh the memory of the whole in my mind. Watching a robot use a ball-bearing pop-gun for target practise. Flooding a smoke-filled poker room. Refueling a diesel elevator from the kitchen food dispenser. Returning stolen instruments to a robotic jam session. Bringing a robotic greenhouse back to life.
Machinarium. If you haven't played it, you should.