Valve hired the developers of Tag to work on Portal 2.Speakercone said:They seem to have borrowed the gel idea from a freeware game called TAG. worth a look if you haven't played it already.
The loading screens in Portal 2 are rather jarring at times. I can only guess why Valve didn't go with their usual method of freezing time for a few seconds while the next level loaded. That method is a lot less abrupt than what they've chosen to do here. There are several instances where you're moving along a seemingly open path and then Loading Screen, only to be transported back to the same path after the loading screen. It's a fairly poor design decision in a sea of inspiration.