I guess I’m going to be in the minority for not heaping praise upon BBEdit’s new update, version 10.[1. See also: MacWorld’s review and IT Inquirer’s review, among others.] However, as a long-time user (I think I started using it somewhere around version 4, IIRC), there have been enough changes in this version to throw my whole workflow out of whack, including one key feature (for me at least) that’s now gone altogether.
Interface
The document drawer has been on the right side of the screen since its introduction.[1. I’m not going to get into which version introduced which feature because, frankly, I just don’t remember.] So for years my eyes have been used to seeing my document on the left edge of my monitor, and a document drawer on my right, which I assigned a keyboard shortcut to show and hide at will. Since I read and write in English (well, HTML and PHP), going left to right, my content was left aligned where my eyes were comfortable finding it.
Now, open documents in the same window are listed in a sidebar on the left, and the document itself is on the right. This may sound like a small change, but now my eyes have to find the left edge of the document somewhere closer so the middle of the screen. The built-in keyboard shortcut to hide this panel is CMD-0 (zero), which in of itself is not obvious, but now this is causing the left edge of the document to shift back and forth.

In short, it’s hard for my eyes to know exactly where the left edge of my content is. Anything you have to think about beyond the code you’re trying to write is a distraction which takes away from your focus. I want the left edge of my content to be anchored to that left edge of my monitor, unmoving. BBEdit should at the very least make the sidebar’s position a preference.
Preferences
One of BBEdit 10’s biggest interface overhauls was in its preference window. Certainly, the preferences were growing out of control with options to customize almost any aspect of the program, but what BareBones chose to remove has left me scratching my head in bemusement. Not to mention the overall design of the preference window itself.
Now the preference window sports cutesy icons in the left sidebar (a Groucho nose and glasses? Really?), renaming almost every category so that I have to go hunting for the right tab. But as I do, the preference window resizes for each category, creating a whole lot of unnecessary movement. More distractions.
BBEdit 10 Preferences from taupecat on Vimeo.
But not only all of that, but some options are now missing entirely from the preferences system. To delete to the right of your cursor (say, on a MacBook [Pro/Mini] keyboard that lacks a right-delete button, you used to be able to set a preference that would make Shift-Delete do that. Now that preference is gone, replaced by an “expert” preference that requires opening Terminal and entering a command on the command line.[1. What’s more, BBEdit’s User Manual hasn’t been updated in quite a while, so it still says, “Holding down the Shift key with the Delete key makes the Delete key work the same way as the Forward Delete key on extended keyboards. This feature is particularly useful on PowerBooks.” Yeah, that’s right, PowerBooks.] [1. @BBEdit tweeted what the shift-delete expert preference command is to @TheMacalope, but I can no longer find the tweet and I cannot find the command anywhere on the web. It’s one of those things you just have to ask BareBones for.]

Another preference demoted to the “expert” category is “Next Document and Previous Document navigate in: Display order/History order” which was in the “Documents & Drawer” preference category. When I have documents open for days at a time, which I often do, the order in which I opened them is pretty meaningless, and accessing them in alphabetical order is far more useful. Now, that preference is gone from the preference window altogether, and can only be set by typing “defaults write com.barebones.bbedit SurfNextPreviousInDrawerOrder -bool YES”. Awesome.

Window Arrangement
This is, by far, my biggest gripe with BBEdit 10. In my everyday workflow, I copy HTML from the browser to work on front-end (HTML, CSS) changes locally, before migrating my changes to a JSP or Java file that might take hours before it’s built, and builds only happen three or four times a day. Traditionally, I used a custom keyboard command along with my preferences to open my HTML file and the JSP file side-by-side, something like this:
In BBEdit 10, such window arrangements are completely gone and the only arrangment left is one window stacked upon another. So a critical function I use each and every day is completely wiped out in the name of simplicity.

There are third-party fixes, such as Cinch and BetterTouchTool, but none of them are as simple and as quick as what I had going in BBEdit 9.
BareBones support has said to me in email that “some of the options may make a triumphant return in a future update.” That’s cold comfort, to say the least.
Conclusion
I’m not going to dispute, or really address much at all, the improvements that BBEdit 10 has made. You can now edit files in a Zip archive without opening and rezipping the file. I don’t remember ever having to need this feature, but it’s probably going to be useful for somebody. And there are interface updates to some of the HTML markup tools, but I rarely used such tools in BBEdit 9 so I’m not sure yet how much that will benefit me.
All I can see right now are the things that are gone, things that I relied on to do my job the way I did it, and overall I’m left feeling like BBEdit is a huge step in the wrong direction for me and my workflow. Since BBEdit 10 came out, I’ve dabbled with TextMate, but that doesn’t have the great CVS and Subversion integration that BBEdit has, doesn’t do the side-by-side window arrangement that BBEdit 9 gave me, and it simply cannot handle large files such as MySQL dumps.
So I guess I’m sticking with BBEdit 9 for the time being.