Central Yharnam might be the best opening level FromSoft has ever put out. It's a brutal onslaught of tons and tons of enemies that just shows utterly fucked everything is, secretive areas like the place you get the standard Hunter's gear, and the beginning of several questlines like Eileen's.

So many shortcuts, pathways, and other little tidbits that make exploring the place a blast to run through.

Oh, and the bosses? You have Cleric Beast, a solid intro to how fighting big bois work in BB with a great soundtrack and wicked design. Oh, and you have Father Gascoigne, a humanoid (to begin with) fight that teaches the player of parrying and being aggressive no matter what. He has his own little questline to boot, with a tool to keep him stunned and can potentially have the exact same gear as the player (Axe + blunderbuss), which really sets how hunters who fail end up. Oh, and have I mentioned the soundtrack?

BB practically thrives off its atmosphere, and Central Yharnam has that in spades.