My view is probably warped because I helped design the PTL "language" for Python. However, it's been my experience if you write well factored code (i.e. Don't-Repeat-Yourself, helper functions/macros), then templates that use the HTML by default mode end up looking extremely ugly. Essentially you end up with mostly Python logic with a little HTML markup mixed in.

It's not friendly to UI designers who like to load it into something like Dreamweaver or translate their static design into the template. I haven't thought of any good solution for that though. Zope TAL seemed like a valiant attempt but I'm sure how successful it was.