1.9.10 is mostly the same as 1.9.9.
Main difference is the switch to statically linked assemblies for SQLite.
Version 2.0 is complete rewrite (more or less, anyway) of the latest 1.x version.
The main differences from the older versions is
A few things have been dropped from the new version.
"Party Mode" and the "Auto Theme" features have been discontinued simply because it didn't seem like anybody was using them.