Had my first trip on a 720 last week from Shenfield to Liverpool Street, about time after having seen them around from bridges etc since last year. Compared to the 321s, as one would expect, very nice. The aisle is a tad narrow and the seats also, but this is still a commuter train rather than a long distance affair. Having said that, the ride comfort, relative silence and lack of swaying and pitching are second to none.
Being able to walk through the train unhindered is also a benefit.
Balance was restored with a 321 home. What a difference!