I hate to focus on what the DM is doing wrong, because it seems he's doing a lot of things right. But, this is what I see:
a) He's not nurturing his players. He's got a 'sink or swim' attitude combined with a propensity to tease (or insult?) his players when they 'sink'. Teasing and gently ribbing your players may work well after they've learned to trust you and when they usually feel compotent to face your challenges, but its a very bad idea otherwise.
b) He's guilty of forcing players to rely solely on player knowledge, and not character knowledge. Presumably the players characters have some knowledge of the surrounding world, it's climate, it's religion, it's political divisions, and history. It's great to have campaign level secrets, but those should be limited to things people don't commonly know to be true. He's trying to elevate every little aspect of how his world works to the level of a campaign secret, and then play 'gotcha' with the players when they fail to understand how a world that exists only in his mind works. That's one of the most common novice DM flaws, and sadly its a flaw that is most common in DMs with great imaginations and lots of potential to be really entertaining DMs. They love their own ideas too well and they misjudge not how fun it is to be surprised, but exactly what surprises they should be springing and when. The 'Sixth Sense' is a good example of how and when you should hit people in a story with the twist. It has to be fair, and it has to have been properly led up to.
c) It's great to throw the players into challenges that are over their head, or which seem over the players heads (but aren't). The former teaches the player to think creatively, and the latter gives the player a sense that he's part of a shining moment of awesomeness when he wins 'despite the odds'. But you also have to put the players in situations where the odds are clearly in their favor from time to time, and you even need occasional situations where the foes are just mooks and pushovers that the characters can shine against by completely dominating. I think he's got a bit too much ego invested in his situations. It's easy for a DM to dominate the PC's and enjoyment of dominating the PC's should be something every DM should guard himself against. Beware any desire to 'show off' to them doesn't prioritize your enjoyment over theirs.
d) The strangest situation was the 'inevitable' execution the PC's fell into. I wonder if from the DM's perspective if it was nearly so 'inevitable'. The reason this story is so odd is that in the same account he's previously provided a cave that the players could shelter from giants, and a dungeon which could be easily escaped from. He's not a DM who seems unwilling to give the players an escape clause. I'd love to know what was on the DM's mind at the time. Did he feel they'd been so stupid that they'd earned a three strikes and you are out rule? Was he dragging the execution scene out for hours in hopes that the players would pick up on some obvious ways to escape that they never picked up on? Where the players actually continually thwarting his intentions by, for example, insulting and antagonizing their jailors or, so that the DM's ability to concieve of leniency was continually being thwarted? From what the player has said, it just seems wierd how this worked out.
e) He's not describing the world in a way that is really useful to the players. Or as pemerton put it, there seems to be a lot of poor scene framing going on. While I don't agree with some assessments that the scenes are bad, I do agree that they aren't being framed correctly to make the players choices meaningful. This is why I'm very interested in the question of whether the DM prepares a lot of notes. If he doesn't, then the answer to why the scenes are being framed poorly is immediate - he's making this up on the fly and so hasn't invested much time thinking about the implications of his choices (notes IME almost always empower the players). If he does prepare notes, then the problem is not so much railroad (as pemerton suggests) but rather a rowboat world. The players can 'go anywhere they want', but have no real ability to utilize that freedom because they lack both a map and an accomplishable goal. Frequent campaign crashes because the players didn't know how or where to row the boat are typical of many sandbox purist games. But yeah, if there are no notes, then we are effectively on rails with a very harsh conductor.
You know, there's a reason why most modern console RPGs did away with the "pixelbitching" occasionally found in early-generation CRPGs.
