Reason seems to be one of those love it or hate it tools for most people and sits in a space that's not quite plugin and not quite DAW. Personally I love it, and have used it since version 4, and have seen quite a few changes in that time.
To me, one of the best decisions that Propellerheads made was to consolidate Reason and Record into one tool, as it made no sense to keep them separate. It certainly extends the range of Reason to give it audio capabilities, and it has a very good mixer.
While third party plugin use has never been a feature of Reason, the Props came to a compromise and brought RE functionality to the table. RE may have failed if third parties had not developed for the platform, but when you look at the respected developers creating RE's, you have to realize that Reason is taken seriously as a platform for them to develop for.
At the core of Reason is a variety of tools that can be routed to a mixer as in any other DAW, but with the advantage that you can easily flip your racks around to patch any device to pretty much any other device. If you have no experience of this on other hardware or software there's a learning curve for sure, but once you master this, you really see the strengths of Reason.
I won't go into the details of each instrument on the racks as it would take up too much space, but Reason certainly has a wide range of instruments, covering various types of percussion, synthesizers, samplers and effects. The Props web site is a good place to start if you want to read further into what is included.
A common complaint that I have heard on KVR is that Reason relies on ReWire to communicate with other software. ReWire is not for everyone, but as it is implemented in most major DAWs and is pretty simple to set up, I'm happy with it and have never really had any issues using Reason and Ableton Live side by side. A recent addition is MIDI out, so that really opens up more opportunities with external instrument triggering, and any other uses for MIDI out.
On the downside, Reason does have a very cluttered GUI if you don't have a large monitor, and gets very fiddly on laptops. I think it is a little difficult to learn coming from other DAWs or hardware, but as with any tool, you can learn it over time.
Solid as a rock as far as stability is concerned and very efficient in terms of processor use. Some of the tools might have a bigger processor hit (Kong comes to mind), but for the most part they are very efficient.
I think it is priced very fairly, and upgrades come in at a reasonable price too.
Yes. A great workstation. I'm amazed at how easy is to create any kind of music style when sitting in front of that luxurious infinite stack of Synths and effects including the new Mixer. The audio stretching is impeccable! And the new effects are able to transform beyond recognition (if you so desire) any audio going through them.