The connection in Brussels is a bit annoying: you only have to change platforms but you have to wait at least 30 min. Removing that connection is I believe critical, as it will gradually save time over the next few years.
The Paris and London Eurostar terminals are nice. The Brussels one is a bit dark and only for 2 platforms. The Lille is alright actually, and only for 1 platform. I'm not sure where they would put it in Amsterdam though (and that might be the cause of the delay). The current Thalys to Brussels always uses the same half platform, but it might be tricky to reserve it for a Eurostar that only travels twice a day. Also, the Amsterdam station has expanded its shopping centre, which leaves little space for a decently-sized Eurostar terminal. I'm intrigued at where they're gonna put it! Maybe build an extension on the water?
For the most part, the train is for me a better experience: less busy than a plane, decent internet, better seats, which all means I can actually work on my laptop. You simply pay a premium for this convenience.
I think both the plane and train markets serve different purposes: cheap but cumbersome or expensive but comfortable.