I think excluding one or two outliers, the "don't lie to someone" principle is an ok one.
Yes, for an oath of devotion paladin I agree. And I can also understand that breaking your oath by lying is probably the easiest thing to implement in-game. I just hope that by the time we get the full game we’ll see a much more sophisticated implementation, including the ability to select a deity and break oaths by going against your faith. I can see that there will be a limit on how far Larian can go with this, but surely they could at least make it that accepting blessings from evil deities, or seeking power from sources that are presented as evil in the game, if you follow a good or neutral god has an impact on the oath.
I also have a lot of sympathy with those who have said that breaking an oath shouldn’t necessarily be a one off thing, at least when the transgression is relatively minor, but not having managed to actually break my oath yet I’m not really qualified to comment on that aspect!