Hard to go wrong with Baduk/Go. Doesn't really scale to groups though.

Terra Mystica[0] and Tzolk'in[1] are both low randomness worker placement game that require long term planning and fun mechanics.

If war-games are more your speed, Diplomacy[2] and Twilight Imperium 3rd Ed[3] are some of the best in class. Both take all day (or more if you play Diplomacy by mail). I personally like Exocus: Proxima Centauri[4] a lot in this genre.

[0] https://boardgamegeek.com/boardgame/120677/terra-mystica

[1] https://boardgamegeek.com/boardgame/126163/tzolk-mayan-calen...

[2] https://boardgamegeek.com/boardgame/483/diplomacy

[3] https://boardgamegeek.com/boardgame/12493/twilight-imperium-...

[4] https://boardgamegeek.com/boardgame/122842/exodus-proxima-ce...