My inlaws are Finnish... the total lack of germanic/romance cognates makes it very difficult for me to remember any vocabulary. But I've never really put in a serious effort to learn it.

The cognates are difficult, true - there are quite a few old Indo-European words if you know where to look (kulta - gold, kuningas - king, ranta from Swedish strand, i.e. shore). That said, once you've built up a core vocabulary, it's quite easy to learn derived words. For example, kirja, kirjasto, kirjoittaa, kirje - book, library, write, letter. By comparison, you can see how much different all the equivalent English words are due to its mixed Germanic and French/Latin vocabulary, and how much a challenge that makes for non-native learners.

Cool examples! I can definitely see how Finnish would be easier to learn than English, assuming a lack of familiarity with related languages.

Greek is also very synthetic, so a little basic vocabulary goes a long way. I like the word for "waterproofing", literally "against-through-rain-making" (αδιαβροχοποίηση, a-dia-brocho-poiesi)

This has been my experience too. For me as a native Russian speaker, the grammar is fairly easy and logical, what trips me up each time is the vocabulary. I speak passable German and Spanish and those two help me a lot with other Europear languages. With Finnish, if I don't know a root/word, then I just don't know it and that's that.