(First person that says "no more prio" gets killed, you've been warned, I will seriously proceed to abuse power in that case.)
The biggest rule difference between OCG and TCG, priority to use ignition effects in response to a successful summon, goes away, as the TCG finaly sold enough rabbit support followed the guidelines of the OCG in correcting one of the game's most non-sensical rule.
In case you don't know yugioh, ignition effects are the spell speed 1 effects of monsters you activate in your main phase when you choose to and have general priority.
Before: you could activate those effects in response to a summon, unlike any other spell speed 1 effect.
Now: you can only activate those effects when you have general priority.
For more information consult the mini-article by konami on the matter, a bit of studying on it would help anyone who is unfamiliar or not very familiar with those things.
What this means for the metagame?
Rabbit.
Now rabbit can be stopped by anything ranging from effect veiler, book of moon, fiendish chain, raigeki break and the list goes on. But most importantly, veiler.
Before we had the veiler and maxx c dileema, maxx c would work on wind-ups and was not completely dead vs rabbit or inzektors, while it was not much help, while veiler would work vs inzektors and wind-ups, but not vs rabbit, which was the top deck.
That would leave people with the choice, maxx c or veiler, leaving decks unable to defend themselves against all the top threats.
What changes now?
Veiler works vs inzektors, it works vs wind-ups, it works vs rabbit. Now with veiler you are fully covered, you can afford to main 3, and that will manage to badly hurt rescue rabbit.
However that does not only change the balance between rabbit, inzektors and wind-ups.
Rabbit as a deck, while it had many strengths, it had uncommon weaknesses that hadn't been in the metagame in a while. Rabbit had a hard time getting over on-field monsters with attack higher than 2500 and indestructable monsters, making any closely consistent deck with high attack monsters good in the metagame because it handled the top threat (see the success of dark worlds and dragons). However with rabbit weakened the metagame will have a greater balance instead of a strong rock-paper-scizors relationship, a matchup has less chances to give you the game or kill you with that.
Now other than rescue rabbit, the decks which benefited from this rule were in fact few. Wind-ups had a small benefit from it, but when you had the card that would stop them (book of moon, effect veiler, etc.) it was more or less the same in the end. REDMD does have the same advantage from this rule but part of its success is attributed to the success of rabbit. DAD is at 1 as it always was and chaos was only here and there. So I wouldn't recommend maxing out on your raigeki breaks, phoenix wing wind blast etc. Remember that what this changes isn't the entire game of yugioh, it affects some decks and mostly rabbit. If you ask me, 3 veilers are good for the current opponents, while the irl metagame switches much faster so what this will bring is harder to predict.
That's all, some facts, and some thoughts from me on this. Don't go crazy, still the same yugioh we played, but with weaker rabbit.
Now on WDA, all ongoing tournaments continue on the same rules they started with, for KP and New System tournaments you still have priority to activate the ignition effect of a monster in response to its successful summon. In case you have to ask, all tournaments after that will of course work under new rules, all official duels outside of the tournaments work with new rules and all rps will work by new rules.
(remember to avoid that phrase, there will be blood)
