XSLT, part 2

The ugly

If it isn't nodes... XSLT's use of XPath is remarkably elegant for a large number of applications, but it isn't especially effective at the kinds of things regular expressions are good at - building structures out of arbitrary text.
No side effects It's just plain mind-boggling to a lot of people that variables can't change their values. XSLT isn't the most approachable creature for programmers used to working with procedural and object-oriented environments.
Debugging is creative Most people find that their first style sheet produces lovely blank output. While that isn't especially terrible, more complex style sheets can be difficult to maintain, especially if an XPath guru concocted them without leaving behind documentation.