[color:"orange"]Our current idea is to connect different levels to each other through specific "gates" where we can stream out the level you were just in and stream in the level you're going to. In those gates, there is gameplay, it's just not so diverse as a level is.[/color]

You mean something like a mountain pass, that you walk through to get to another region?
If gameplay is relatively open and the world immersive, that's all that counts. Dungeon Siege was very seamless, but the world was very linear and IMNSHO very boring.

[color:"orange"]On the topic - Oblivion/NWN/Baldur's Gate load in the interior of houses as different levels. Gothic doesn't. Both methods have advantages and disadvantages - which do you prefer ?[/color]

Like most others I'd prefer house interiors not be separate levels. If the load time was short I wouldn't mind if they were, however.