As an integration specialist, I work with many clients in the ecommerce industry and have been working with many order and channel management tools over the years. There are many tools out there and many more are coming to the market yet Linnworks stands out for three main reasons.
A. Simplicity. Clients are shocked these day at how fast I can get them up and running with full integration of their various channels. The screens and menus in LW are maximized for usability, you don't get a gazzillion buttons on the screen, it's all compiled into context menus (the ones that pop up when you right click). Flow of the screens are left to right, top to bottom, unlike other tools I've worked with, it's easy to figure out what button to press next. B. Flat fees and no contracts. Many tools out there charge a percentage fee of sales and that's a big problem for sellers who compete on Amazon with very thin margins. LW charges a very fair monthly fee and they also work on a month-to-month billing system with no contracts. This forces them to stay relevant with their feature set and takes away the risk from the sellers. C. Powerful Scripting Engine. Let's be real. Every system falls short somewhere regardless how great it is. LW also has some shortcommings but they have a script engine (C# based) that makes it possible to customize the application and add any features needed right inside the system. They have many sample code that can be easily adapted. I am using the scripting engine to manage sales tax, integrate with QB (using OpenSync for QB), and generating custom reports.
What's still missing is inventory transfer features (done for now by exporting and importing CSV files), integration with Stamps.com (in development, they say), CRM (they work to integrate with ReplyManager to handle this), and some more features they're either working on or planning to add in the future.
Support is also great. I never had to wait for more than one business day for a reply.