Short answer - it is not. Adobe is always torn between noble aspirations of creating unified design / development software and the less elevated urge to make money by selling that same tool as multiple products. Hence the ongoing parade of various stiffs, headlined by ImageReady and closely followed by Fireworks, that have either gone to oblivion or are on the way there. Adobe Muse awaits a fate no different.
It is a wonderful program for individual designers who are comfortable with cleaning up code, just as Dreamweaver was a great visual tool for budding web designers some 15 years ago. You can work in Photoshop and import to Muse or work directly in Muse, generating a page or entire site. As a creative, you will have access to Adobe Edge Web Fonts, libraries for menus, forms, and widgets, ability to implement comprehensive metadata including Google Analytics, and can pretty much build and publish a simple site from the ground up without additional help.
It works for personal and small scale projects, where budgets are either nonexistent or such that any HTML issues or discrepancies between different browsers can be overlooked. Resulting page code is not optimized and will require significant time expenditure on development side, which would not work in agency environment. Do not expect the site to be fast, ADA compliant, or anything else beyond visually pleasing.
In conclusion, Adobe Muse is a wonderful tool for creating a simple web presence. It will be continually evaluated by Adobe against similar products, Parfait and Edge Reflow, both of which will be covered by us in coming days. Adobe will not maintain a stable of competing software products, cannibalizing each other’s market share and will eventually decide on the keeper. Adobe Muse, now in its second year of public release, will not have a long life as a standalone product, as continuing costs of keeping it compliant with newer browsers, bug fixes, and support will not be on par with revenue generated by individual designers doing small scale projects. Best case scenario is that some of its features will be folded into whatever revolutionary design / development software Adobe will put out next after it discontinues Muse.