One thing that I find gratifying and frustrating at the same time. I'm still learning in my Sounders/USMNT save and I'm 13 years in. I often make mistakes I'll realize at the time or a few months later and I have to live with those, just like in real life.
For instance, the 6 months prior to contract end = free transfer...well, that's how I lost Ozzie Alonso to France
Or the time one of my Sounders academy players was a dual national (US & Mexico) and Club America signed him when he was 16. Never expected that. (Lucky for me, game crashed and I was able to rectify that). Now I check the Nationality of every academy player. If he's dual national and halfway decent, I sign him to senior team, then loan back down.