I also just watched Interstellar during the weekend, and I think I have some answers to some of the plot holes Bltizo has raised.
-Why did the initial Ranger leaving earth need a rocket booster if the Ranger shuttles could leave the other planets through VTOL/direct ascent on their own power? Of course if the other planets have a small radius (even if they have 80% or 130% earth's gravity), then the escape velocity of the Ranger shuttle could be correspondingly smaller. That said, this is a smaller issue I have, because there are ways to explain this. I just feel like they wanted a dramatic "leaving" sequence
The planet with 130% of the earth's gravity on surface with a smaller radius would require larger escape velocity than on earth.
I think the rocket booster sequence can be explained in a sensible manner that they wanted to conserve fuel for the entire mission as much as possible. So while the Ranger shuttles will be fully capable of lifting into space from Earth, fuel spent by the shuttle and thus of the mission cannot be replenished.
-Shoudln't it have taken Cooper months to retrain and learn the mission, instead of just leaving right on cue?
I think that was implied. Otherwise how did he become all familiar will all of the controls on the shuttles and the ship?
-Are the Ranger shuttles frigging water proof?? Why?? And are they able to survive a mile high tidal wave and still fly?
They are space reentry vehicles, have airtight pressure hull and structure and outer casing to repeatedly withstand the torture of reentry. Waterproofness is therefore a given, if it is not even waterproof how on earth can it be qualified as a mannable spacecraft.
-Why did the inside of the Endurance's stasis pod room look like it was an old bathroom, with chipped paint and everything? Wouldn't the interior of such a vessel seek to minimize tiny floating particles that could damage circuitry or enter individual's mouths and noses?
I think the movie tried to paint a picture of Earth in its last days with Human material wealth in rapid decline. There was a lot of hint of Science and Engineering being neglected and underfunded by world governments, since people could barely feed themselves. That could be the reason for the "cheapness" seen various sections on the ship.
The ship has artificial gravity (though centrifugal force) which is supposed to run constantly right from its first start, which minimises risk of floating particles. Under such artificial gravity, the crew should be able to eat normal food instead of relying on the toothpaste like stuff the contemporary astronauts have.
-Introducing 5th dimensional beings/humanity in far future in the end is the ultimate dues ex mechina, especially for a film that has tried to be so realistic. I'm left wondering if everything else prior to Cooper entering the blackhole was thus pointless, because it felt like everything was just a distraction for Cooper and TARS to get the blackhole's data
Not really. They needed to find a habitable planet. And their main mission was to find the planet and populate it with gene seeds from Earth. The blackhole data was a sidetrack mission.
-Why did the 5th dimensional beings choose Murph's frigging bedroom as the vehicle of communication for Cooper?? Are the future 5th dimensional beings that fond of symbolism and poetry? Couldn't they have created a tesseract that allowed Cooper to interact with a blackboard in (adult) Murph's office in NASA or something? that way he could have simply written out everything on a blackboard instead of having to translate it via morse code to that stupid watch.
This for me was one of the major plot holes in the movie. And there isn't really a good fix. First of all the morse code idea just cannot work---see below. The blackboard idea may be more plausible if Cooper was also a theoretical physicist who studied the gravitational equations. But he isn't one, and the theorists need the raw data from the blackhole to fix some of their base hypothesises. This is most likely to be numerical data, and cannot be written down by equations. If he could, then he would have solved the gravitational equations himself.
It is also clear from the plot that the 5th dimensional beings cannot communicate with either Cooper or TARS. So they cannot have given the equation to Cooper. And if they could, then why bother with Cooper at all, can't they just contacted the professor Brand in his NASA office in the first place and given equation to him using the blackboard method?
-Why didn't earth send another expedition through the wormhole in the years after Endurance left, or even after Murph solved the gravity issue?
I think it was implied that they did send ships through the wormhole after Murph solved the equations. They also must have established contact with Brand on the inhabitable planet. And only after that did the migration start.
I think the reason they did not send another expedition through the wormhole during all this 30 odd years after the Endurance left was somewhat also explained by the plot.
First reason is probably funding. NASA was pretty much a clandestine organisation at the time, and they probably gathered much of their approved resources for a one-shot Endurance mission. Another mission would take another several decades, if it is even approved---which makes it consistent with the 30-odd year time frame.
Secondly, Prof. Brand never really expected the Endurance mission to return. The most important part of the mission to him was the cargo of Earth gene seeds.
====================
For me the movie did a very good job on the wormhole, conveying the mathematical notion of a three-dimensional hole, which does not exists in our everyday life. This is far better than the type usually portrayed in Sci-fi, like that in Star Trek Deep Space Nine. It also managed to make the time paradox in the relativistic theory look and feel natural, which I am quite impressed with.
The a big plot hole that I find they cannot get away with is that Cooper transmitted the entire TARS's blackhole data to Murph using MORSE CODE.
Just think about it, the contemporary particle collider experiments produce gigabytes, even terabytes of data (I have worked on some of those during my undergraduate days). MORSE CODE has a transmission speed of ONE CHARACTER/NUMBER (one ASCII character is 1 byte) per SEVERAL SECONDS. Even if the data is only 1 MB in size (a single MP3 song is about 3-5 MB, a single HR photo in compressed format is about 10MB), it would take well over 1000 hours (1456 hours if every character took 5 secs to transmit and note down) to transmit and record the data. That is 60 DAYS if Murph does it 24/7 no rest, no eating! And if the data is in a more likely region of several gigabytes or terabytes, then Murph and her offsprings would have been long died before the transmission could even reach halfway stage.
Also aren't they in hurry of leaving the place, as Murph has set fire to the corns and it is burning its way to the house? And for Cooper to remain in contact Murph and the watch has to remain inside her bedroom.