Ubers like Dark weapons and such don't really exist, generally they fall similar to things such as 100 Souls (Similar to Excal with a different special) and Arrest Needle (spread needle but stronger with more reliable paralysis). There are no uber weapons like Rainbow on SCHThack with the exception of Psycho Bridge (stronger Dark Bridge) except the resistances to ultimate enemies make even that a little bit underpowered. Things you should know: Maximum stats to characters have been increased (Exact stats I'm not 100% sure of). Drop rates are all put into a drop chart list that can be found here:
http://phantasystaronline.net/droptable.php
Unlike SCHThack, PGF is only available to hunt over christmas rather than year round, although our christmas event tends to last several weeks. GMs occasionally host mini events that can trade PDs or other items for specials on weapons including all Yasminkov, Type, and S-Rank weapons. Donations (done in the form of Donation Tickets) can be used for trading, redeeming items, adding stats to weapons, etc. etc.
We also generally have more events in the game, such as Triforce and Anniversary events. Certain weapons are also combo locked (Master Raven, L&K 38, Snow Queen, etc.) that you may not have had locked on SCHThack.
This particular server also occasionally (every few days as of late) partakes in events known as Happy Hours, where for three hours, all rare drop rates are trippled. Others can post if I missed something big, but that's most of what I can think of.