Loving the game. Played it with the partner and there was a lot of discussion about the mechanics which is only ever a good thing.
We had two 'runs' - first time round our starters were 2 x unlucky + 1 x talkative and the second was much better with 2 x introvert and 1 talkative. The 2nd one went by much faster, but that's partly our fault for having all our units bond, so unlucky stacked very painfully.
Some of the traits are just... Worse than others. Or better than others! Heroic, Fierce, etc are obviously preferable to Shy, Unlucky, and so on. This isn't a bad thing, per se, but it means a substantial cast of characters are best left on the shelf while you wait for a better one to pop up. Sharing traits with them is detrimental, even if it's only going one-way with a full 4-good-traits character, because ultimately you can and will have better characters -- it's just up to RNG how soon.
If there were some way of switching out traits it could be really awesome. Or an option to replace them? (Sorry if there is - we didn't notice one.) Switching between the summoning exp ones for grinding and then throwing out the Mega Units for the big fights, etc.
TL;DR: loving the game so far!