Yes. Some instances will block (known as defederate) other instances, so you won't see any users or posts from those instances. Some instances disable downvoting. Many are similar to each other.
Lemmy.world is the everyman instance though, so you will get the broadest look at the fediverse.
Some instances will be topical themed, such as mander.xyz (science), or programming.dev. others have political and aesthetic leanings: lemmy.dbzer0.com (Anarchism, AI and cyberpunk aesthetics).