The invisible blocking (they weren't really walls, just weirdly placed blocks everywhere) was definitely cumbersome. I like to get off the beaten path and explore every nook and cranny, I ran into them all the damned time. It's really annoying seeing something cool over the horizon or a room that you just get blocked off by.
Generally speaking, I've found that how much a person spent on Rage largely corresponds with their feelings about it. Most of the Steam Sale types seem to think its pretty good for $5-15, I haven't seen many people who think it was a good deal at $60 though.
Anyways it's all academic, we might never see a followup since it really underperformed and id is working on internal engine and support tools for the rest of the company now.