Both the US and most other western countries have a reasonably good separation of powers. Also, the US and other western countries both are clearly the most attractive places to live in the world. And democracy is a large part in this.
However, in both cases there are worrisome trends. It is as if they got it organized reasonably well and then stopped improving and started backsliding. There are many things that the western democracies could do better.
To name one, the huge and ever-expanding regulatory state is severely harming democracy in both Europe and the US. This tends to be seen as a talking-point of what is called the 'right' (but, indeed, mostly a talking-point, as opposed to an action point) and as such does not need more elaboration but it could be a talking-point (but often is not) for what is called the 'left' as well by noticing that much lobbying is involved in creating regulation and that the outcome is therefore not going to be in the citizens interest. Regulation is where the executive branch is sitting in the chair of the legislative branch and because of this the citizens have little influence.
To name another point, western countries have been far too friendly with countries that have a very bad human rights situation. I think that taxes on import should be proportional to the amount of human rights violations and other failures in democracy that a country has. That way every improvement that a country makes regarding to human rights immediately leads to a financial gain. The US being so very friendly to Saudi Arabia is just terrible. I think this is a thing that if you keep it up for a few decades it would enormously improve the lives of people all over the world. Note that this is also something that takes away discretionary and rather arbitrary power from the executive branch by basing the policy in a very simple and objective law instead. I think one could gain votes by campaigning for this. And this is what law should be. Simple rules that feel like they are discovered rather than invented as opposed to rules so convoluted that only the executive branch has the means to write them.
You talk about the difference between the US and other western countries. Many things could be said about this but one thing that seems to be on most peoples mind in regard to this is that the US has less social security and some European countries have quite a bit more. Well, I think that is mostly an orthogonal issue to the point of democracy. The respective peoples of respective countries can choose for themselves the amount of social security that they consider to be correct. Let me say that from a democratic point of view it is much more acceptable to 'bail out' citizens that get into trouble than to 'bail out' banks that get into trouble. The latter being a prime example of where lobbying has led to a situation that is in the interest of the sector being regulated and not at all in the interest of the citizens.