I’m not quite as negative on Scripting Bridge as others, but that may only be because I haven’t used it as heavily. It works OK for my purposes, but it certainly seems unfinished, and I’m not satisfied with either the exception- or delegate-based error handling.
For a while, it seemed that AppleScript, with good framework and bridge support, could become really great for both users and developers. Instead, it’s kind of been in stasis. We have Automator and AppleScriptObjC, which didn’t really live up to their potential. And XPC is the new hotness, but (so far) it’s solving a different and narrower problem.