Hey I actually had more trouble with the player controller this time. It's very difficult to tell what resizing the player will do, whether he/she will phase through the ground (which I later discovered to be platforms). I know that tutorial levels are annoying, but I couldn't recommend anything for this game except a that. Or at least finding someway of communicating the main mechanics...
A huge recommendation would be listening to the Portal commentary, which you can turn on in-game. You will start to get a sense for how Portal makes tutorials fun. But I wouldn't go any further until you get that tutorial biz figured out!
Cheers,
Steven