Seven problems in US elections

1. Primaries. They're fixed in such a way that different states matter different amounts for different parties' candidates, and in some cases, the primaries either don't matter or, in areas with by-party primaries and landslide support for one or the other party, decide all too much.
2. The electoral college. Contrary to popular opinion, the electoral college amplifies the effect of large states and makes small states matter less. In practice, since politics is regional, this means a few states have disproportionate leverage and gain special treatment from presidential candidates.
   
3. Plurality voting. There are tons of better alternatives, from instant runoffs to the Borda count to approval voting.
4. "Third party" candidates. See #3 - there are better ways to do elections that aren't nearly as vulnerable to the spoiler effect, but while you have a plurality election, third party candidates have at best the effect of trying to make sure that the two major parties don't completely ignore their radical wings.
5. Campaign finance. There are good things about the system in place, but that doesn't mean it can't still be fixed.
6. The public polling horserace. I like to follow the polls just as much as the next person, but I think sometimes we spent too much effort trying to figure out what groups are "key" to an election and who will win by how much.
7. The median voter theorem applies to public perceptions, not reality. We really could use better honesty, accountability, and more clearly differentiated options that don't simply talk past each other in code designed to reach the base and bypass the moderates.