What's different here:
You earn virtual tokens called STEEM that can be traded for Bitcoin, which can be traded for US Dollars
The whole system is open source. If someone wants to censor steemit, a new steemit clone will pop up somewhere else on the internet. The blockchain (the database that stores this info) is all over the place and shared.
Freedom of speech is a lot easier on steemit
Here people are incentivized to comment on your posts, and vote you up if it is a good one. Here both readers and content creators both can earn something for their time.
I could go on and on.. but these are some immediate differences.