I have used them extensively and I quite like them. Unfortunately when you ask this kind of "what's your favourite HMI/PLC" type question in here you get all manner of noise, and rarely much useful information.
First up the question of price. You can buy cheaper HMI's out there. If however you are buying in volume, or you can access a reasonable discount then bear in mind AB are a premium brand, but have room to move.
RSView Studio 4.0 is now a lot more robust than it was at V3.0 or 3.1. However you will need to pay attention to the install requirements, as Studio is a Factory Talk application that makes extensive and intensive use of MicroSoft's .Net framework. This will require that your OS and version control is 100% clean. Just slapping Studio on some old laptop lying around the workshop is not likely to be a happy arrangement.
Bear in mind that RSView ME (Machine Edition) is the baby brother to SE (System Edition) that is a full-blown distributed global database, multiple server HMI. The FactoryTalk concept implements a true "Publish Once, Subscribe Many Times" paradigm. At least that is the marketing hype. And to give RA credit on this, they usually do deliver on the hype. When ControlLogix was launched it was met with some scepticism that it was going to meet it's goals...and so it has.
However some new users have made the mistake of thinking that because the PV+ runs Windows CE as it's OS, it looks like Windows and can do all maner of HMI things...that is must have all the features and performance of a full-blown HMI running on a server class PC. Well it isn't. It is perfectly capable within it's specs.
One area where it is not a full scale HMI is the relatively limited macros. If you cannot do it with the standard functionality, then there are quite limited possibilities to program it in with code.
However PV+ has lots of nice features, but the ones you don't find everywhere else are "Direct Tags" and true "Global Objects". Direct tags eliminate the tedious job of building tag databases...PV+ accesses the PLC addresses directly eliminating the need for an intermediary database.
Global Object is V4.0 are seriously nice and hugely improve editing productivity.
Also I should add that the PV+ is probably best used on Ethernet connections. Other networks are supported and various non-AB protocols are supported via third party OPC servers, but for your first project out the door, talking to an AB PLC via an Ethernet port is the easiest learning curve.
I have to ask what exactly you mean by "user editable values" though. I can think of several possibilities, but I can't quite grok any of them at this end.