All in one integrated platform.
The costs are indexed on revenue (pay as you grow) and the editor is committed to the success of the customer since it starts billing only when the customer is online and selling. The platform is very complete, customer friendly and performs decently regarding speed. Demandware is targeting brands and covering most of their needs, as well as understanding the key factors that a brand need to manage, and where it usually falls short.
Since I'm a technical expert and not an end user, I'll impersonate a brand when answering the questions. (I very well know the platform though)
The language used in the platform is proprietary, making any former internal workforce useless until retrained. The page load time is, on average relatively slow. On most references they showcase, the pages loads around 3 to 4 seconds, which is higher than most platforms.
The product offers large customisation capabilities but is still SaaS driven, what you need and is not built in needs to be built by yourself. The multi channel part is not yet totally optimal even if large progress were made with DSS (Digital Store System) and the rendering speed of the page is not always constant or as fast as other products.
The timing before being in production tends to grow, passing from 3 months previously to 6 now and growing slightly because the SI's working with Demandware tend to be flooded with demands. Also, the ecosystem is a bit weak, the platform do not so much drive external companies or freelancers to develop tools/addons, which, IMHO lacks a bit.
Check if you have specific needs that would not already be covered and would be a bit tricky to "side develop", then other platforms like Hybris could be logical to review, especially if you are very multi channel oriented. If you are a brand, looking for an online solutions covering most of the usual needs, Demandware will most likely cover the vast majority your potential needs.
Look also into the already existing systems you need to interface to Demandware. If they are very usual and widely spread on the market, Demandware most likely cover them, if not, you may enter a slight turbulence zone to make everyone talk together properly.
I'm not a direct user of Demandware, but I extensively reviewed the product since I'm the author of the "Benchmark of ecommerce solutions". The 2014 version will include the review of Demandware, hence I worked with them (in Paris & in Boston), to their review.
I do like the "all in one" approach, tailor made for brands. Experimented people, logical in their approach and the product is very complete. New features like DSS are covering the holes and the points that were ont previously covered pretty quickly and the roadmap is being drafted along with customers.
The overall approach of the product is very attractive and the SaaS model, adopted a long while ago made them breach the UK/US market first. It first limited the expansion in the EMEA zone, mainly in the Latin area because people think they can beat the odds and lower their TCO. In US or UK, the mindset is different because the accountability is made in an analytic way, hence the US/UK were the first to adopt. But the trend is now reaching Europe as well, and the French team has been replaced and rebuild for example, showing that when Demandware identifies a problem, it reacts and correct quickly.