I've been away from HS for a year or so and I wanted to get back into it recently. The last expansion I really played was Descend of Dragons, later I played a few games of Outland and tried the new Demon Hunter, but mostly did Battlegrounds. After that I lost interest in the game. Seeing now how it changed a bit I would like to pick HS up again.
So can anyone tell me what are the major changes so far? I don't understand the whole Core thing, what cards are now the mainstain no matter the year, what cards should I invest in, is it worth to buy the Welcoming bundle or what's its name and so on. Any tips are appriciated.
First of all, welcome back. The core set is just something everyone gets as long as all classes are at level 10. They'll change every new year of Hearthstone. There's not much I'd recommend investing in, but control Warrior is in a really good spot right now, so if you were to invest into a deck, I'd recommend Clown Warrior. If you're more into aggro, Hunter is in a really good spot, as usual. The Welcome Back bundle is definitely the best bundle they've come out with. It's designed to be "worth it". You don't have to invest into any of the core cards because you'll get them all for free.
You can disenchant your extra copies of the Core cards if you need dust, but keep in mind you won't have them when the Core set rotates.
Also there's the rewards track now, which gives you some good value if you don't have the battle pass. It's easy to level up on, but I always just buy the pass to get more stuff and level up quicker. Do I think it's a good purchase? It depends on how often you play and whether or not you want extra cosmetics.
The cards you have from the Basic and Classic sets are still useable in Wild and in the new Classic format (which is the game as it was back in the day) so don't disenchant cards if you intend to play either of those formats.
As for what deck to craft, i would suggest you read a meta snapshot and decide for yourself, because everyone has different ideas as to what is strong and to their taste. Vicioussyndicate.com is my preferred meta analysis.