If you watch the beginning of that lengthy 3 hr keynote speech Carmack gave recently, he admits one of the key problems with RAGE was not just the ending. They kinda misleadingly advertised it as playing like an RPG, so a lot of people assumed it would be a 20 hr game that was really fleshed out with RPG elements, but it played more like a linear shooter with some crazy, repetitious racing thrown in. Frankly I don't see how expansions are going to fix that. It needs a LOT of free DLC to change the way the game itself plays, and it will never get that.
The ironic thing is, they spent LOTS of time making the game, so naturally people expected something less superficial in the end result. The more Carmack tried to explain away the length of development though, the more it became obvious that the real problem is the tons of little mistakes their team makes, which add up to wasted production time, and it took him WAY more time to say that than it should have. At first he tried to excuse it by implying people want more detail in games than most notice, but then the talk of numerous mistakes (many in communicating code used), made it obvious what caused the length of development.
In short, Id has some good ideas (except for megatextures), but they aren't very efficient at implementing them yet. Hopefully they will improve on that, because it sounds like they need to work on it a lot. I gotta say though, if they stick with this ridiculous megatexture concept, I, and many others, aren't going to have much confidence in them.
Check it out 
