I promised a review so I am going to do my best, but like many things it is just something you will have to experience yourself to make the best decision. I would have liked to been able to A/B with a "comparable" device, but the logistics of that have proved more difficult than even my pessimism may have predicted.
Build quality: The thing looks like you paid a thousand dollars for it as you take it out of the box, and the design is fantastic. All of the input/output jacks are high quality and the switches and knobs are a tactile dream. Longer use will back up or negate all of this, but for now I couldn't be happier.
Latency: 1ms at 96Khz and 128 sample buffer size. This is on a laptop, 2.4GHz i3 with 4 gigs of RAM, a barely middle range computer that can be had for around $400 USD brand new. It will play all of the demo songs without clicks or errors at these settings. Let it be noted that others are having trouble with DSP usage on V6, and I am not implying that Balance will help you in any way (although it may).
Sound: Wonderful. Obviously I am not claiming to be some expert, and as I already mentioned I am unable to A/B, but I have used a number of different interfaces over the years. Too my ears it sounds as good as anything I have used. I have used Presonus, Apogee, Mbox, MOTU, Lexicon, whoever made those Event Gina PCI cards, Focusrite, and probably some other junk that I don't even remember at various home studios and with gear I borrowed or bought off of Craigslist and then sold for twice the price later on Ebay. There is something about the Apogee (duet "1" I believe) that I really liked - possibly more than balance but is hard to say. Being that I can't afford a decent mac I (and many others) am never going to own one. The only other gear approaching my subjective wonderful was some MOTU gear I played around with some time ago, but that was also noisier (probably due to Firewire). It is really quiet when you aren't making noise and being a guitar player I can say that the preamps really bring out the nuances in your playing, I find myself needing to process the heck out of things to cover up all my mistakes that it picks up so clearly.
Intangibles: No breakout cable/box, no external power, no buggy control program, no buggy mixer program on top of the buggy control program (these last two "features" are the primary reasons I chose the Balance), some people might like "clip safe", easy as sin to use, just plug stuff in and go.
The Bad: As they might apply to various individuals.
No MIDI I/O, I didn't need it as I use my MPD26 as an interface for other junk but this might be a sticky point for some people.
No S/pdif: I would have liked to have it since that is how I have always brought my guitar in (through GT-8), but there isn't a whole lot going on with this nowadays (or is there? I don't know.)
Only 2 ins/outs at a time. I only record one thing at once, like many other home producers/singers/songwriters/etc. But if you want to record the whole band at once you will either need an external mixer or a different interface.
Seems kind of expensive. But nothing else delivers the total package (with Essentials) at this quality, and at this price point (IMHO).
In conclusion, Balance with Reason Essentials is probably directed towards individuals interested in getting into (quality) home recording without having to go to school to be an audio engineer. Sure those cheap Mbox with pro tools le or se or whatever might be a less expensive and a more widely used(?) alternative, but they don't provide the quality or features and Pro Tools will make somebody that just wants to record their music quit making music (kind of speaking from experience). I think it is a good inclusion to the probably already-glutted market, but might turn some away (beginners and people not making money off of music) with its price, and others (pros/recording engineers) because it doesn't have enough I/O and includes software that they might not even really use (or maybe they will
For somebody getting the free upgrade to 6 from a previous version sans record this is definitely a buy (if you want the upgrade...and why wouldn't you?). As you are getting the interface for about $349 USD in that situation. It is definitely worth that. People that got the upgrade for $1, however, might have trouble justifying whether it is really worth full purchase price and should probably wait until the pros do some real reviews, and/or the price drops or it becomes a separate purchase. It is very likely that some will conclude that the interface is worth all of the approx. $500, but I can't make that judgement at this time.