How much has changed since 8.5?

Tricky to answer, totally new GUI which consequently changes the workflow but still pretty much in the same Cakewalk way.  If you go for the producer version the Pro channel will be a real revelation.  Download the trial give it a whirl. 

It's so subjective... the engine is better; the UI  is different. You may like it more; you may like it less. Either way, there's a learning curve. Your cheese has been moved and it'll take some effort to find it.
 
On the plus side, many bugs have been fixed in the compatibility and interoperability domains. Some VSTs that were glitchy in 8.5 are now solid.
 
I gripe at the (subjectively) stupid UI changes from the 8.5 family, but the fact I use X3 and have never gone back should be some kind of testimony.

Go into it with eyes open...it's like if there was a new start-up company that unashamedly ripped off major parts of 8.5 but wrapped it in a (at least IMHO) better GUI, improved functionality/workflow, and placed more of an emphasis on stability. 
 
That's the good news. The bad news is that if you try to duplicate 8.5 workflow in X3 you will be frustrated. Often there is a different workflow that is much better (e.g., comping) but you need to learn it. I think the people who have had the greatest success transitioning from 8.5 to X3 have realized they need to "unlearn" 8.5 as well as learn X3.
 
Bottom line for me is you lose some time investing in the learning curve for X3. However, you more than make up for that time the more you use X3. I had 8.5 and X1 installed at the same time but never went back to 8.5; even with X1's birthing problems I still got projects done faster.

It takes a little time to adjust from 8.5 to the X series but IMHO the effort is well worth it. I loved X1 from the outset and just gelled with it. I'm not a new user either, I started with V2.
 
The whole interface is much more sensibly laid out and as a result much faster to work in. Screensets alone are a revelation and there's so many improvements since 8.5 it'd be hard to list them all.
 
The best thing you can do is download the demo and go into it with an open mind and spend a little time re-learning the "new" ways. I'm sure if you're prepared to do that you'll find it time well spent.

>> how could you know? You say you don't even have it and no longer use X1 or X2.
 
I assume Mike tried the demo and watched the YouTube videos, like the rest of us.
 
Some of us prefer layers. It's very subjective.

stickman393
>> how could you know? You say you don't even have it and no longer use X1 or X2.
 
I assume Mike tried the demo and watched the YouTube videos, like the rest of us.
 
Some of us prefer layers. It's very subjective.

Maybe so but if you read a review and it turned out the reviewer only had a demo of Sonar X3  (which we may not know for sure) would that have an impact on how thorough you thought it was and perhaps it relied on what others have said? Then add to that the reviewer has never liked any X series Sonar what would be your conclusions?
 
Mike has been consistent in that I can't recall any positive statement regarding the X series from him. Maybe I have missed some of his postings but even if I have it would be rare if he did.   
 
The fact that he is commenting on a product he does not have to a member asking if he should buy it or not bothers me. It may not you or any one else. I think it is wrong to do that. 

You may satisfy yourself with thinking that comping is quicker with the "comping" tools but I find that you can not comp as precisely as you can with Layers so for me it has seemed like a step backwards.

 
Comping in X3 is way improved over how it was in X2 and earlier versions. Accuracy hasn't changed at all while speed of both auditioning and applying edits  is way faster, using either speed or manual comping.
 
If you'd like to post up any problems you have with comping accurately using the new tools and methods I'm more than happy to help, although I guess if you're not interested in using X3 that's probably a redundant offer.