Emmett,

All the seats are leather, the difference is that First class has 2 & 1 seating, so you get a wider seat and I believe a bit more pitch. Not positive about the pitch.

First class also see attendants on hand to bring you any food you want, as opposed to your having to walk to the cafe areas within the coach cars. However, it should be noted that unlike Acela First Class, the food is not inlcuded. You have to pay for it by credit card, no cash accepted. The only difference from coach is that you don't have to go get the food and carry it back to your seat. They bring it to you.

The shuttles are timed to the train, so there's always one waiting when the train arrives.

Finally, I believe at present top speed on the NEC is still 100 MPH. They are hoping to certify the cars for 125 MPH, but I haven't heard that's been done yet. However, even once the cars are certified, the diesel engine on that train is only certified for 110 MPH, so that will become the new maximum for ACES.