Here are some thoughts:
1. 260 miles in 4 hours, average speed ~65 mph, maximum speed 100 mph. That's pretty much faster than anything Amtrak offers, except the Northeast Regional between New York and Washington. And with cheap, conventional used equipment on conventional right of way. This is probably what we in the US should be shooting for as a first step, not full-on high-speed rail.
2. Tickets are a fixed price, not to exceed 30 euros. That's nice, no more fiddling around trying to outsmart yield management software. That's what you really need to do if you want to maximize train passengers and get cars off the road.
3. No food service, even for a 4 hour ride. Doesn't seem to scare people off, as there seems to be places to buy food at the stations.
4. For all Thibault was complaining about the sorry state of the rolling stock, as an Amtrak customer, I thought it wasn't too bad. I think that even the non-matching seatcovers were an intentional design. The seats had no recline and apparently less eat pitch than an Amfleet 1, but they looked reasonably comfortable. The overhead luggage racks looked a bit small compared to Amtrak's, but they had several off-the-floor racks throughout the coaches. By the way, the Ouigo high speed train had an interesting 3x1 seat configuration. That means that single travelers have a better shot at getting a single seat without a seatmate, and parties of 3 (like my family) can all sit together, but it also means that more passengers will get stuck with the dreaded middle seat.
5. Suburban stops are an innovation?! That's one that Amtrak has long had over the French.
In all, it looks like a good service, and maybe Amtrak should emulate some of the concepts for their corridor trains and the Northeast Regional. Maybe a business class car for people who want some more legroom, and I would think that a cafe car might do all right on a trip this long. I hope it's successful.