FM 12 improves over FM 11 in many ways, most of which are good and add to the overall experience.
The new contracts system lets you lock certain aspects you think are non-negotiable. For example, locking the weekly wages of a player may result in his agent asking for exorbitant appearance bonus. It's a mildly interesting feature, but it helps keep your budget under control. That being said, there's still naught you can do about negotiating contracts with your staff.
Tone has been added to player interaction. It makes a minor difference and you'll have to play around with tone to figure out which tone your team best reacts to. The game never fully explains and I think it's all a matter of trial and error more than anything else to get the tone right. Player interactions could help improve your relationship with your players and result in you being in their favoured personnel list.
Staff interactions, however, are rudimentary. There's nothing you can do to improve your relationship with your staff, and this is quite annoying. Similarly, there's very little you can do to prevent other teams from poaching your best coaches except perhaps try to offer them a new contract and hope they stay. However, training players for preferred moves now happens through coach interactions, and it helps because the player cannot refuse to learn a new move.
CORE GAMEPLAY -- Remains the same, pretty much. You can now ask your team to familiarise itself with up to 3 tactics, which probably helps for home/away/difficult games. You set your tactics and play, and if you've got good players playing in the right positions and with the right tactics, you'll probably do well. That being said, the game's biggest problem, right from the beginning of the series to now, is that it's a game based on probability. Except possibly for some bugs or glitches, if you've won too many games on the trot, you will probably lose the next one. It happens. Sometimes, it just feels contrived. And though it may count as cheating, when you quit the game before restarting it and play through the match again with completely different tactics, you will still end up seeing the same result most of the times. It just gives you a feeling that it's all been scripted on the whole, and all you're doing is filling in the details.
SUMMARY -- All in all, FM-12 remains a good football manager simulation, probably the best there is. If you've been playing FM all along, there's no reason to stop now. And let's face it, if you've been a fan of the FM series, you're not going to stop playing. Just go along for the ride. It's a fun one.