Major improvements, takes the best of 2004 and 2005 and adds a little bit of its own.
In 2005, the main gripe was the passing game. Receivers dropped easy passes, CBs jumped 30 feet in the air, etc.. In this versions, receivers don't drop nearly as much, but they still drop passes. Coverages have been tweaked a little bit. And the Matchup Stick is back, which was a great addition in 05.
The running game is still lacking a little. When you hit a hole, a DL will sometimes come out of nowhere and tackle you.
The AI still needs a little work, granted it will never be perfect, but there are some faults this year. Example, if you blitz a linebacker inside of a DE, the TE will not block anyone and the OL will try to get the LB, giving the DL an easy path to the backfield.
If you are going to play this online, be careful. Find people you know and play them, cheesers are all over the place. I never play anyone online unless I know who they are because there are a lot more cheesers than last year.
Overall, 2006 combines the best of the past two years along with many great improvements to make this game the best one yet.