What's unique in Polkadot?

I'm curious, what exactly makes Polkadot stand out from the rest in the cryptocurrency world? I've heard about its interoperability features, but I'd like to know more. How does its architecture allow for seamless connectivity between different blockchains? And what kind of advantages does this bring to its users? Additionally, I've also heard that Polkadot aims to solve scalability issues. Could you elaborate on how it plans to achieve that? Lastly, with so many cryptocurrencies available, why should someone consider investing in Polkadot?