Lets start this topic in a traditional way of taking on both side of parties positive and negative:
XBAP or WPF web application is a great enhancement and is no way comparable to Silverlight. XBAP is lot more bigger and opportunistic than Silverlight. XBAP is like building any other desktop application in WPF except that the app is published on web or even on a system by setup. It is quite simple and easy to use. Programmer can go for Full trust mode to access all the local client resources (with clients permission) else for with partial trust so that only certain basic functions like reading a file from client but not writing a file to client. A lot of security options are given by default under Dot Net.
XBAP is good in many ways, the main issue is with Microsoft on how it is promoting the technology. The main drawback when compared to flash etc. is that XBAP applications are blocked in IE9 under default settings.
XBAP is best choice to serve the clients under the given conditions that if they enable the option to run XBAP in IE by changing the settings. Following is the method for changing to desired settings in IE:
Open IE and go to Internet Options as illustrated:
Then, go to security tab and go for custom settings:
Then go for changing to desired setting to enable the XBAP to be available in IE as follow, the default option is disable, now it should be changed to enable as follows: