What exactly were people's complaints with the system?
Because from what I personally found the only issue I ever ran across was the whole "Finding/Joining the RP" process, because of all the bumping messes and what not.
But once one actually got into the RP itself?
Then I found it was just a flat out improvement, with organizing and information storing being so much easier.
I'll go ahead and list off complaints I saw both in the roleplay system feedback thread that was made in the Help Desk area and that people told me directly via Skype and PM.
The system adds useless bloat and information segregation areas to one on one roleplays and many (perhaps most) group roleplays. Only a portion of group roleplays actually made use of the system in ways that were more extensive than just using the [tab] code or spoilers in the first post of the OOC. Given that this means it's useless bloat for a majority of roleplays, it's kind of awkward. Also, all it really has over using BBCode for organization is that for GMs it's a tiny bit easier than using spoiler code and a little more simple than using tab codes, but for players it isn't effectively much different than having tabs/spoilers that fulfill the functions of a cast list and rules area somewhere in the first OOC post.
It didn't even do the main thing that a thread-linking tab system is good for: putting all the related threads in quick and easy access from one another by way of a push of one button from any page of any other thread. You can go from any page of the auto-created thread for a group roleplay to the Overview or the Cast List or whatever, but you can't get to the IC. The IC is a mostly separate entity. To get from OOC to IC without bookmarks or signature links or whatnot you have to pop over to the Overview or w/e tab, then hit another button on the right (or down below after scrolling past stuff on a small screen) to open it up; to get from IC to OOC without any linking not enabled by the system you have to go to the roleplays section and just find the damned thing. We already had an in-site bookmarks feature that could get you from anywhere to one of your bookmarked threads in two button presses, which equals the efficiency of OOC to IC navigation in this roleplay system and absolutely trounces the IC to OOC navigation it provides, so using it instead of bookmarks was a net loss for ease of navigation.
The system confused newcomer GMs a lot. It was not at all intuitive for a roleplay creator to figure out how to make a roleplay and then link other threads to it. We had to put up a big notice that showed up at the top of the roleplay areas to explain how it works, and even with that AND a guide I wrote to explain it as plainly as possible, people were still confused a lot of the time and had issues.
This system is kind of shit for people on mobile devices with data plans, because instead of popping open an in-post tab or spoiler to see the cast list you've got to load a new page entirely.
The fact that the roleplay system sorts roleplay listings by creation/update day makes it not just a pain in the ass to find and join an RP, but also to keep the section clean by finding and archiving dead roleplays.
Using this system killed our intuitive content tag system where we had prefixes for subgenres and such in each genre section, exacerbating the problem of trying to find an RP you want.
Interest checks and partner searches got the shaft big time by going from being subforums attached to each roleplay genre to being big pools where all interest checks for groups and all partner searches for one on ones were thrown into big pools. This combined with the lack of a good content tagging system meant that finding a roleplay from that angle was also a pain in the ass.
So, in summary: it made things obtuse where before they were intuitive, ease of navigation (a key selling point to a thread-linking system) was worse than what we already had in place, it was a threefold problem for finding and joining new roleplays, and the only thing it actually added was bloat that is at best a little cleaner than things we already had in place. As Diana put it in the announcement: "the issues and bad problems completely out-weighed all the good stuff."