First, I want to be clear... player mood only affects contract negotiation. There is no "team chemistry" or "player is upset so he plays worse"... yet :)
Additionally, I am aware of concerns about micromanagement. I don't want it to be essential to micromanage this stuff. If you want to ignore player moods, you probably can get away with it without suffering too much. If your team is successful, players will want to play for you. In a big market? Even better. That gets you most of the way there. It's not like "players who want to play in a big market will only play in a big market" or "players who want to win will only play for an established title contender" - in addition to not being fun, that wouldn't be very realistic either. You can also disable player mood traits in God Mode, if you want.
With that out of the way, take a look at the UI for the new mood system, from your roster page:
...
There are 3 things you see are their mood score, mood traits, and probability they will be willing to re-sign.
The probability they will be willing to re-sign is based on their current mood. It is not a projection of what they might think when their contract actually expires. So for a player with some time left on his deal, this number can change.
Mood traits give players a little bit of personality. There are 4 possible values:
- Fame (F) - Player prefers a large market, an engaged fan base, and lots of playing time.
- Loyalty (L) - Player wants to stay in one place for a long time, doesn't care much about market size, and doesn't like to see you trade away too many of his teammates.
- Money ($) - Market size and team success are not very important, but nice team facilities give a little boost. Least likely trait to refuse to negotiate.
- Winning (W) - Team success matters a lot. Willing to accept less playing time and a small market.
If you click the mood button, you see a popup with more detail, including the individual components that sum up to the overall mood score:
...
Currently these components are:
- Market size - players generally prefer bigger markets.
- Facilities - based on your facilities spending over the past 3 seasons.
- Team performance - regular season and playoff success.
- Hype - viewable from the Team Finances page, this is how excited your fans are.
- Loyalty - players who have been on your team for multiple seasons might be loyal to your franchise.
- Trades - if you trade away tons of players, free agents will be wary of signing with you, since they might be next!
- Playing time - players want to play, so if a player doesn't get enough minutes (either due to tanking or because the team has too many other good players), he will be annoyed.
- Rookie contract - players on rookie contracts are eager to sign their next contract. This gives BBGM something like the NBA's restricted free agency, because it results in your drafted players being less likely to refuse to re-sign.
In addition to those categories, a player's overall "value" influences how likely he is to refuse to negotiate with you. A bad player will be happy to sign with any team, even a team that he actually hates. Good players can be more choosy.