I don't understand people who claim it's a "mindfuck" movie. The plot is pretty straightforward and self-consistent. What it is is an extremely well put-together movie.
The runtime of that movie is 148 minutes-almost two and a half hours. Yet it doesn't feel that long. It also manages to have three different groups of characters doing separate things, without confusing the audience. The last move I can recall trying to do that level of simultaneity was The Phantom Menace, which failed horribly at that task. Therefore, I find Inception to be a very interesting movie intellectually, because I think it's fun to think about the techniques that Nolan uses to make a 2.5 hour, multithreaded movie so entertaining.
One glaring inconsistency that tripped me up for most of the "climax" of the movie was the amount of time Arthur had in "Level 2" while the van was falling...
The bridge looked to be about 100 feet up when the van started falling. It takes 2.5 seconds to fall 100 feet. So Arthur, who was one "level" down, would have had 2.5x20 seconds to figure out what's going on... come up with a plan... go back to the floor below to retrieve the charges... get back to the floor where the team is... get them wrapped up and moved to the elevator... set the charges... and finally detonate them. That took _way_ longer than 50 seconds.
Sadly, I actually did a little more research after the movie and found my estimate was even a little generous. The bridge the van was falling off was the Commodore Schuyler F. Heim Bridge in LA. Combining the published stats on the bridge with a clip from the movie (http://www.youtube.com/watch?v=k_4qc-JYZPo#t=17s) makes it look like the van only had ~80 feet to fall...
Your explanation reminds me of an experience I had watching Bill & Ted's Excellent Adventure with an old girlfriend's roomate.
About halfway through, he started making these little dismissive groans and mumbling "no way" under his breath. They gained volume as the plot progressed until finally he couldn't take it anymore:
"No way. There's just no way they could fit that many people into a phone booth."
I actually felt the pacing of the climax was a bit messy, probably due to the time dilation, but it felt like the higher levels had little relevance. I also found the snow scene to be the weakest part of the film, probably because it was completely different from the urban environments of the rest of the film so it felt forced and jarring.
Your example of The Phantom Menace is interesting because I think the simultaneity was actually one thing that was done well in that shambles of a movie. IMO it was the poor characters and direction-less plot that failed that climax, not the editing of the different scenes.
There's a reason Inception was so popular. It was very easy to follow for just how convoluted it was. The average consumer of Hollywood just can't ever hope to follow Primer, but they followed Inception well enough to debate it, or want to see it a second or third time.
The runtime of that movie is 148 minutes-almost two and a half hours. Yet it doesn't feel that long. It also manages to have three different groups of characters doing separate things, without confusing the audience. The last move I can recall trying to do that level of simultaneity was The Phantom Menace, which failed horribly at that task. Therefore, I find Inception to be a very interesting movie intellectually, because I think it's fun to think about the techniques that Nolan uses to make a 2.5 hour, multithreaded movie so entertaining.