Tumblr has never really lost its wide variety of customization. I'd argue it carried on the Geocities and MySpace individual touch. If you go from one personal tumblr to the next, they often vary to a great degree in atmosphere, color scheme, content posted, purpose, layout, etc. You also still see all the expected bizarre design choices, broken layouts, etc. that one would expect given that. Being able to customize it to a large enough degree to give a sense of one's personality, was one of tumblr's primary appeals to its large younger userbase.
Though it might also be worth mentioning that Tumblr is a total pain in the * to use precisely because of that customization. Every dang page is different and I never know what to click. Worse, Tumblr is so slow that every wrong click is an expensive loss of time and patience. On the rare occasion that I find a Tumblr worth following, I just use the RSS feed because the site is too frustrating.
