Just saw it again myself and some thoughts:
The totem/top has a noticeable
favor developing in the axis of it's wobble. I.E. it looks, and sounds, like it's going to fail. I didn't really notice much difference in the kids but, I suppose, they looked a bit older and that Cobb sees their faces and he couldn't in his dreams/memories I think says a lot and he also says that he couldn't stand to live in a dream world as it wasn't good enough for him.
The drugs made the dream "time dilation" much more severe, a factor of 20 in the first level, IIRC. Dialogue in the "Goldeneye 64" level suggests that the deeper levels were the standard 12, probably because they'd be using a standard sedative? (This is noticed when at one point Cobb says that the guy in the Zero-G Hotel level has a "couple of minutes" to initiate his kick giving them in the GE64 level "about 20" this suggests the standard 1:12 dilation and not the 1:20 the drug was giving them.
The protectiveness in Fischer's brain caused them to improvise their plan. They expected to have around a week in the first level (the city level which I'm going to call the GTA level to keep with our video game theme
) but the immune system forced them to have to do it inside of a couple hours as opposed to the time they originaly would've had.
The heavy sedative meant that killing themselves wouldn't work, thus the need for "the kick."
Wantabe doesn't get injured in either the hotel level or the Goldeneye 64 level but as his injuries worsen in the GTA level they begin to manifest themselves, and hinder him, in the deeper levels.
The "time dilation" is tougher to compensate for in the deeper levels. As I said upthread the hotel level and the Goldeneye level both move at "normal time" compared to the slow-mo of the GTA level while Leo and Ellen are in the Limbo level (which was Cobb's dream). When Leo and Ellen are Limbo the Goldeneye level should be moving 12-20 times slower and then another
12-20 times slower in the hotel level. The only way I can reason this is that time isn't passing on the G64 level or hotel level when we're not watching it. A scene ends in one of those levels, we watch another one, go back, and pick-up where we left off. Only the "GTA level" is occuring when we're not watching and its time is so off that it appears to us in slow motion.
The only explantion given for the dream-sharing machine is that it was developed by the military for traning purposes.
Wantabe, because so much time passed from him "dying" in the Goldeneye level and when Leo goes down there it seems that decades had passed. The time dilation between Limbo and the final dream level must be vastly dfferent than the other levels.
Leo put the "inception" in Mal hoping it'd convince her to leave Limbo. He didn't know it'd grow into the idea of her thinking the real-world is still a dream. He does this by spinning her token in the safe, she had put it in there laid down which is what probably convinced her to think of Limbo as reality and want to stay there.
The idea seemed to be that one would spend so much time, ages, in Limbo that when they woke up in the real world the real world would be so far forgoten they they wouldn't be able to re-adapt again. Leo and Mal, possibly, got around this by being together or by the "short" time they spent in Limbo (around 50 years as opposed to centuries.)
It seems that the "kick" being timed precisely wasn't completely
necessary just the most ideal way to do it. Leo says he has to find Wantabe and that'd he find his own way to kick himself "awake" through the levels back to reality.
Wantabe says he'll keep his promise and Leo, as a young man, talking to Wantabe reminds him of this which, perhaps, helped Wantabe not be in PVS when he woke up in the real world.
It's not made clear what everyone did once they woke up in the GTA level as they'd need to wait out for the sedative to wear off, again after as long as a week. They either hid-out from the immune system during this time or killing the immune system in the lower levels somehow got rid of them.
I had to laugh seing the standard video game "+" medical box (with a defibulator!) in the "Goldeneye" level.
The Goldeneye level was supposed to be the maze to get to vault room, Emma and Leo's right-hand man has developed a short-cut through it just in case which was used when their time was cut short.
This movie has got some serious
twists and turns in it but, damn, it just makes my mind spin as I just get off on this kind of mind-bending stuff.
Excellent movie, well done, Nolan!