There are a lot of toxic communities on Tumblr, unfortunately. It's a bit of a minefield sometimes, especially if your work happens to touch the more toxic circles, so that's a consideration.
Sometimes the site has technical issues, but that's not too major a problem. Every site has issues. Even Tapastic. (Some might say, especially Tapastic...)
Some of the more extreme corners of Tumblr have invited negative reactions from other sites and communities, but that reflects as poorly on those other communities as it does on the Tumblr users who may have caused the situations.
Original artists tend to be overlooked on Tumblr. It's hard to get any notice unless you're a fanartist hopping on whatever bandwagon of the moment people there are on. If you just want a creative/art blog and intend to build your readerbase in a way not dependent upon Tumblr's userbase, that won't matter anyway; you'd have to do something similar with a Wordpress system or Blogger.
Basically, Tumblr is just an easy-to-use, free microblogging platform. It's not really fair to judge the whole site for a portion of its millions of users, most of whom joined the site because of its accessible usability and refreshingly relaxed rules. But it is good to know the pros and cons of any site before becoming a part of it, whether or not you ever interact with the rest of the users there.