It seams like you left during the Arcanyst Vanar meta (which is quite understandable). Since then Circulus was changed to a 1/1, Bandai Namco showed up and changed the names of many cards as well as introducing Diamonds and banning several countries from playing Duelyst.
The latest expansion gave Zir’an multiple ways to create Hallowed Ground (a tile like Shadow creap except it heals you for 1 at the end of your turn instead of damaging your opponent) most of them are quite nice cards IMO (although you might want to take my advice with a grain of salt because I don’t play Healynor).
Vanar mostly quit playing arcanysts and switched to walls, they got luminous charge a 5 mana summon 5 0/1 walls that blow up on you if you kill them and Flawless reflection a 7 mana card that when comboed with Ghost Seraphim lets them turn a lot of walls into Ghost Seraphims with rush
Songhai sometimes use their old decks (8gates, one woman army) sometimes they play other decks like midrange Songhai and the new mantrahai which (tries) to abuse the new card Firestorm Mantra (6 mana Steal 2 health from the enemy general for each spell cast this turn) and abjudicater to do some flashy combo and kill you from 20 health (assuming they pull off the combo properly).
Vetruvians got azure summoning which lets them make a big combo that summons 3 skywings and 3 Dragonlarks for 6 mana, usually the aforementioned combo is used in golem decks which have became quite popular lately. They also got some new obelysks and a way to undispell obelysks.
Magmar is mostly playing the same decks they were when you left.
Abyssians play aggro almost all the time now. They got Phantasm (2 mana 3/2 whenever your opponent summons a minion give a random minion in your action bar +2 attack) which leads to 10+ attack tigers if left unanswered.
I tried to point out the most notable changes since you left although I probably forgot some stuff. If you have any questions feel free to ask and someone will answer.
Overall, the Meta now is much better than it was when you left, and I hope you will enjoy Duelyst.