I play and have played every single madden much more than I care to admit. The game is full of holes and glitches that become painfully obvious during online play. I'm incredibly disappointed there's basically zero improvements to online franchise which is pretty much the only thing that will allow for prolonged interest in the game. However, I will purchase it because I'm a little Madden bitch.
So far I haven't noticed a ton of improvements. Packers offensive playbook is almost identical with the except of a "hailmary" package and a few extra plays. The defensive playbook as a few more wrinkles, but still pretty similar. I hope the custom playbooks mitigate the overall lack of widely variable plays.
I don't know what to think about the dynamic player performance yet. That will take time. The demo is a little strange with no commentary and not being able to play with the depth chart. However, two things I'm liking so far is the improvement of zone coverage and speed doesn't seem to be as big of a factor as M11. Offline franchise apparently has a ton of improvements but playing the computer all the time becomes boring as hell. Not sure how that can maintain ones interest. Either way, I usually dislike the new Maddens when they first come out until I have some time to adjust.
I'm finishing up season 10 of an online franchise in M11 currently, but as I play more of the demo I'll try to post more thoughts. Click the links in my sig or hit me up if you're interested in some online franchise play in M12.