Considering all you have to do is have presence in the tunnels (like always) the tunnel part really didn't change much, except making teams have to be more aware and less just camping one tunnel entrance.
If you really think 'teamwork' is what won Field before this, you're about as crazy as the rest of them. Field was usually won by beating your head against the wall till either A) GDI killed the HON after a 2 hour seige, or B) that ONE person stopped camping the tunnel just in time for a rush to come down. That's pure and utter luck, not really teamwork.
The map was terrible. It had more wins via surrender or changemap than actual wins. Unless you're counting when it's like 8v8, then Field was playable. But only having one stupid, 90 degree angle turn vehicle entrance, plus 2 tunnel entrances that can be camped from one spot in the base to deny everything was not even remotely a good map design. In a 20v20, most Field games were just decided by which team got the most bored people first, as defending against 'teamwork' was piss easy because it was just clusterfucks of people jamming themselves into narrow choke-points.
Also... you're overwhelmingly outvoted on whether new or old Field is better. The only time it 'feels' worse is when it's like a 5v5, since there's actually options now, and one person can't stop literally everything.