We've used a few of these HSTs at different times, and as others have pointed out, Japan's Shinkansens are best by far for space, comfort and convenience and reliability.

Only problem with the Shinkansens is that the fastest and most convenient Nozomis cannot be used by JR Pass holders - and there is no flexi-pass option. In some cases only the Nozomis have a through train option, Tokyo to Hiroshima for example.

The Thalys (the "Red Train") from Paris through Brussels to Aachen and Cologne was excellent for comfort, quiet and speed.

The German ICE trainis were generally very good. We rode from Cologne to Berlin at a fast 250kmh and hardly seemed to be moving. Travelling from Dresden to Brussels via FRA was more comfortable as there was no overcrowding. Language can be a big problem in Germany at intermediate stations as train configurations are sometimes reversed and we don't understand announcements!

Eurostar is fast and comfortable but feels a bit cramped. But what takes away from the Eurostar and made us say "never again" was baggage handling. Their security handling acts like an airline but offers no checked baggage. Passengers have to lift their heavy baggage onto high conveyor belts to be examined by security.