You can ReWire pretty much any DAW into any other DAW these days, so I wouldn't really call that much of a special functionality of Reason. And I still think that the lack of VST support pretty much cripples Reason from being a very complete package. Yes, in terms of really crazy synthesis, you can do quite a bit with Reason, but if you wanted to write an orchestral score for a movie or something, your best bet would be the Orkester ReFill, which, frankly, isn't even all that great compared to the East West Quantum Leap stuff. And besides, Reason can only act as a Rewire slave, so whatever you Rewire it into is going to likely be more fully featured anyway.
Secondly, for a guy who's just getting into computer music (as I presume the OP is), I really don't see how a modern tracker like Renoise would be a poor choice. It's cheap, running around $72 US these days, and has a pretty active community willing to help newbies with learning the program and finding some free and relatively good instruments and VSTs. It's not as visual as something like Reason, but if they haven't been spoiled by the eye-candy, I don't see how that makes much of a difference
Honestly, Renoise is my first tracker, and I don't really see how it's a very limiting sequencing environment at all, as long as you don't play too much stuff in live. Then it gets a little messy with all the delay/velocity/volume column entries. I'll admit that a piano roll is a lot cleaner, but I think the tracker view is a lot faster for guys working without a MIDI keyboard. Saved me another 70-odd bucks I was going to spend on a nanoKEY.
As for Reaktor, I feel like that's great for guys who just want to make some really wild sounds and effects, but you can't really sequence much with that. And I don't think it does ReWire, and Reason doesn't do MIDI out, so you're stuck with one or the other if you buy it, whereas Renoise could load Reaktor and sequence whatever monstrosities you've created.
Anyway, I'm not really saying there's anything inherently wrong with Reason. I'm just saying that I've since moved on, because Reason doesn't really offer the kinds of things I need - namely, some degree of third-party expandability, a sequencer section that better suits my workflow, and a lower price point
The only thing that's bugging me about Renoise is the rather poor support for long audio tracks like live vocals or guitars. But then, Reason did that pretty poorly too, and I didn't feel like shelling out another $200 to fix it with Record. I figure the Renoise developers will have that fixed in the next version, which should be out pretty soon.
Props to REAPER, though. Haven't used it myself, but I've heard very good things. I might invest in that if proper audio tracks aren't incorporated into Renoise with this next version or so. Then I could do sequencing instruments in Renoise, and do recordings in REAPER.