Let's get the disclaimer out there: I'm obviously a big Cubs fan. Overall, I'm really enjoying the game this year, outside of some bugs.
However, one source of frustration is the lack of updates to pitching windups and batting stances. To stay on the topic, Anthony Rizzo and Kris Bryant are slightly off and haven't changed in three years. Rizzo crowds the plate like a mofo, and on the game he's way off of it. Kris Bryant has a much more spread-out stance than what is depicted in the game and his arms are bowed out when he actually keeps them tight.
These are not nearly the most important things to fix, but every little bit of realism added to the game makes a huge difference for me. I'd love to see more frequent updates to batting stances like they did with Bellinger and Gallo last year!