It's a good question. It's a little hard to explain, it's more of a feeling. Some of the touchstones are Rainier Beer (long gone), the hydro races (kinda loved to death), the I90 "bulge" (gone), the Pike Place Market, the Bite of Seattle (loved to death), Bumbershoot (loved to death), Ivar's Restaurant's silly TV ads (Ivar died and is much missed), the freeway ramps to nowhere getting torn down, Bellevue turning into a glass towerscape, Ballard losing its norwegian flavor, Capitol Hill losing its counter culture due to escalating real estate prices, moldy waterfront cabins replaced by $5m mansions, the 1940s bungalows all disappearing, etc.
The Space Needle and the creaky squeaky Monorail and of course Sylvester are thankfully still there and going strong.