Alot have changed there is no elo baned cards now, there is the new EFC elo mode where the higher you climb the lower the cards you can use in a deckm, new clans where added also new keywords, and the old op cards are still great but it depends on the clans that you play, also there is a new game version and there is a pc version on beta atm
Well, I'm not too sure how long you've been gone, but we've gotten a new clan recently and a couple new keywords: Equalizer and Xantiax.
Equalizer does some effect that is multiplied by the amount of stars that your opponent's card (i.e. Equalizer -3 opp attack against a 4* card would be -12 attack and against a 5* card would be -15 attack)
Xantiax is basically the same as Victory or Defeat, just in less words and only found on Xantiax Robb Cr currently. Essentially, whether you win or lose, you will perform some action at the end of the round.
Truth be told, a lot of older cards are still very meta relevant depending on the clan you are playing. For reference, one of my best decks currently is T1 All Stars which all of my cards are about 2 or more years old. Regardless, there is still a lot of ways that you can accumulate clintz and get some of the more recent cards since MNB packs have a lot of high cost cards currently with Quetzal and Maana Cercei still in the pool.
Also, depending on how long you have been gone for, Arcade has also been added to the game and has become a effective way of earning Ld cards, if you are willing to deal with the AI. They have added several Lds as Arcade specifics which unfortunately now cost lots of credits to unlock, but you can still unlock some of the original Lds you might have missed over time through the later Arcade seasons
I think I touched on most things, but if you have any further questions, feel free to PM me