Although based on Jekyll, Pretzel has some differences with it and some limitations.

Pretzel doesn't have collections, but it has DirectoryPages

Pretzel support Razor based syntax in addition to liquid: use --template=razor or --t=razor

Pretzel support LESS by default (and soon SASS)

Permalinks have some additional options

Pretzel does not use Rouge for syntax highlighting

Data Files are supported but currently there is one limitation regarding CSV & TSV files: if there is only one record in the file it is treated as an object, so the notion mentioned over at jekyll does not work as expected.
But there is no limitations for json & yml.