What have they done?
New account holders can no longer create Basic accounts.
Note that this only applies to new accounts. If you've been enjoying a "Basic" (what was, in my day, called a "Free" account and required a friends code... back when this were all fields) account for a while and never wanted to plaster ads over your personal journal or flist, then you continue doing so.
Personally, this is not the massive betrayal that drama-whores are pretending it is. Far greater was when SixApart started plastering ads all over the site's infrastructure rather than only in ad-supported journals. Anyone who thinks this is worse can blow me. Imposing ads on those who have paid to not see them (on the login page, f'rex) is worse than saying "you can use all our features and see some ads, or get rid of the ads and get some more features for $20". It's the same as subscribing to RPG.net or SA or anywhere else that lets you pay to get rid of ads.
Or you could just use a browser that comes with built-in ad-blocking, because ads turn a site's readers from consumers into a product that is sold to advertisers.
But yeah. Not yet as evil as 6A.