In short, geom_bsd and geom_mbr are the things you're used to from sysinstall. gpart is a reworked partitioning class, which adds support for more partition schemes.
There are some rough edges
, mostly with gpart and the old scheme.
It's best to use gpart only on disks that are partitioned with it for the time being.
You may want to add your encswap problem to the bugreports, though I suspect it's the same or related to the fsck problem described in above mentioned thread.