I always find this a bit weird, you only get to choose between two parties. The difference with China doesn't seem that big, they only get to vote on one party less.
But you have more than two parties don't you? Not that it matters, more parties don't have significant advantages. It's just that there is a bigger pool of crooks.
I think it does matter. In the Netherlands you are able to vote right wing without the religion, or even vote on a religious left wing party. There are party differences between how we should handle a lot of different issues. It is easier to find a party you agree with.
Party sizes vary greatly after elections which means politicians feel the consequences of their actions. It is not perfect of course, but it is better.
The weird thing is that it is possible to have multiple parties in the US, but they never get enough votes. This makes it seem like their has to be a lot of corruption.
It matters, similarly to haow it matters that you have more choice in Internet providers than a binary choice of either 1) cable or 2) telco-provided DSL.
Countries where multiple parties feasibly compete have the possibility, at least, of a disruptive new party taking share.
The American system, like the American ISP market in most of the country, is so rigged for the two corrupt incumbents that you basically always have a choice of light dark gray or dark light gray.
I live in Japan where we have a wide range of competing ISPs and political parties. Both Internet service and political representation are vastly better than in my native USA.
(Admittedly, the former more so than the latter...)
There are institutional and legal barriers to third party candidates. It is disguised pretty well but is obvious when you know what you're looking for.