So I am a little hesitant to ask this question because it is so subjective, but reading both Greek and Roman sources, I always got the impression that Greek thinking and way of life, despite its deep influence on us, is very alien, while the concerns and attitudes of the Romans seem very modern in some sense. I do not mean that one is better or worse, just the impression you get reading them.
Recently I found a quote by Nietzsche that says something similar:
To the Greeks I do not by any means owe similarly strong impressions; and — to come out tight with it — they cannot mean as much to us as the Romans. One does not learn from the Greeks — their manner is too foreign, and too fluid, to have an imperative, a ‘classical’ effect. Who could ever have learned to write from a Greek? KGW VI, pp. I48f. [Twilight of the Idols, “What I Owe the Ancients,” sections I, 2].
And this is coming from someone who had a profound admiration for that civilization.
So I wanted to know: a) whether this is something that has been noticed by historians reading the sources, and b) whether anyone has come up with an explanation for this.
Could you give an example of how the Greeks come off as 'alien'?
I think I see where you're coming from with this question. You're right of course that it is subjective, so obviously I shall be giving my take on it, though endeavouring to keep it grounded in observable historical trends. As a caveat, I have come at it with the assumption of a European/western perspective.
One aspect that I think comes into play is the division inherent in study and appreciation of the classical world, namely that Greece and Rome were so very different. On a basic level, Greece in the Classical period was made up of hundreds of poleis, for the most part independent of each other, with their own political systems and fairly small and localised populations. This is very unusual for sovereign states today. Rome on the other hand, a multi ethnic, multi religious, large state with far reaching political institutions is closer to modern states. Tying into that is the fact that these Roman institutions often existed at least in name in more recent, or even our own, times.
For this we must look to modern intellectual traditions. In the late 18th and the 19th centuries, the artistic, literary, and political movement Romanticism embraced the world of Greek myth and history. Poets like Keats and Byron and Shelley examined the Hellenic ideal, some of them fought and died for Greek freedom against the imperialism of the Ottomans. Romanticism embraced the individual, their spirituality, and their creativity, and their freedom to pursue these things. They saw these ideals as those of the Greeks (rightly or wrongly).
This was in contrast to the prevailing European political forces of the time who were highly engaged in imperial conquest abroad and maintaining order at home. What better ideal to aspire to than the supreme might of Rome? Generals were portrayed as emperors in sculpture, the title of emperor was itself revived, and Imperial symbols adopted - I'm looking at you Monsieur Bonaparte... (But not only him). Of course it was the politicians not the poets who created and maintained political institutions that last even to this day.
Another reason is the influence of language. If you speak the Romance languages (French, Italian, Spanish, Portuguese et al) but also English then you will come into contact with Latin on a daily basis. This is true of Greek too but not to the same extent. There is an informal but generally pretty sound rule that says that for everyday things in English there will be an Anglo-Saxon word. There will probably be a Latin word (via French usually) that refers to something related, perhaps more precise or technical. And there may be a Greek word which probably is a technical term. They are in that order usually increasingly unfamiliar, unknown, or just more rarely used. Take this:
Tree
Arboretum
Dendrology
You could do this with any number of examples. Eg Old, ancient, archaic. Often you find you can do Anglo-Saxon and Latin quite easily without ever finding a Greek equivalent. Take mother, father, and brother, with maternal, paternal, fraternal. We might not use the Latin origin words every day but they aren't unfamiliar.
The last point I would make is that unless you are Greek/Turkish southern Italian/Sicilian, or from the Black Sea then the Ancient Greeks never made long term or widespread settlement in your part of the world. In contrast, if you are from Europe or North Africa or the Middle East then the Romans lived where you live, and probably for several hundred years, and your ancestors lived under them, or fought them, or maybe were them. This bit is subjective I know but I think that does make them feel a little closer for some people.