Having recently finished the book Darth Bane: Path of Destruction I had a few thoughts on the matter of the Sith in the Star Wars univers, Palpatine (and Vader) in particular. There may be a few minor spoilers in here, but I'm not going to be talking much about the book itself so it shouldn't have many. These are simply rambled out from my mind, in no order whatsoever, and are based solely on what I know.
Palpatine is probably the most interesting Sith in the entire Star Wars universe because he is the only one who actually succeeds, unlike the others who tried (and in some cases can very close) but failed. At first glance it seems that he adheres to the philosophy of the Sith that Darth Bane sets down better than most others we see. However it is clear that he deviates somewhat, and that the philosophy itself is somewhat flawed, both of which lead to his eventual demise.
"Two there shall be, no more, no less. One to embody the power, the other to crave it."
The first part of Darth Bane's philosophy is the so called Rule of Two. This was first spoken, interestingly enough, by Yoda. How he learned of it is a good question in and of itself, it doesn't seem that he could have read or learned it anywhere. Why not? Bane's goal was to make the Sith appear extinct to the Jedi. From what we hear in the movies he seems to have succeeded, none of the Jedi are willing to believe that there is a Sith Lord out there until Qui-Gon dies. Since Bane himself devised the philosophy, and he had the Sith disappear to the Jedi well enough to make them doubt one of their own, how exactly did Yoda learn of this rule?
I don't plan to delve any deeper into that question, however. This is about the Sith and Palpatine, not Yoda's connection to them (interesting as that may be, it's all supposition until something is written about it). A cursory examination of Palpatine's behavior seems to show an understanding of the Rule of Two. He never has more than one active apprentice at any time. He fulfills his role of embodying the power (especially towards Vader, who's entire reason for joining the Sith is that he seeks some of that power for his own use) and his apprentices seem to crave that power. Well, most of them do. Dooku doesn't appear to have much interest in the kind of power Palpatine possesses, but Maul and Vader both desire that power for their own reasons.
The area in which Palpatine seems to differ most from Bane's views is in his lack of respect for the title Darth. This is understandable before the Empire, as he can't very well call himself Darth Palpatine, the Jedi were somewhat blind, but that would be a clear tipoff. However he seems to prefer the title Emperor after the Jedi have fallen, something that I doubt Bane would have approved of.
It's this use of the title Emperor that shows one of Palpatine's fatal flaws, he depends more on his soldiers and admirals than on the force. The Death Star is nothing compared to what some of the Sith were capable of (collapsing stars anyone?) yet it is what Palpatine chooses to use. In the end Palpatine seems to cast off the role of Sith Lord, and take on the role of Emperor completely.
The main problem with Bane's philosophy, even when it so elegantly handled by Palpatine, is that it fails to acknowledge a simple problem. If you gain power through deceit, betrayal, and cunning, how do you keep it from those who would deceive, betray, and out think you? The Sith had plenty of methods to kill, and plenty of ways to gain power, but no method of keeping it. Even the story of Plaguas tells this, with all his Dark power he had no way to ensure that he could keep it. That is the fatal flaw of the Sith, and the problem Palpatine faces once he becomes Emperor, none of the methods he honed and perfected for years can work as soon as it is well known (at least to his enemies) that he's a Sith. They'll expect betrayal, be prepared for deception (or at least they should be, they kinda mess that up in 6) and know his power.
"At last we shall reveal outselves to the Jedi. At last we shall have our revenge!"
Darth Bane took the Sith underground so that they could make full use of their abilities. Darth Sidious brought the Sith to the forefront, and in doing so robbed them of those abilities. Yet he did so in a manner that Bane would have approved of. That seems to be the fatal flaw of the Sith, they seek that which they cannot possess (at least not possess indefinitely) to the exclusion of that which they can possess. They inevitable try to grab that which they cannot hold, true power, and in doing so leave behind their power. As soon as the Sith step out of the shadows they become easy targets (relatively, compared to how hard they are to hit in the shadows). Yet they cannot help but step out of the shadows, their entire philosophy is based on letting their emotions go.