Blizzard has announced "The Raven Bundle" which is being sold for a limited period. For $10, players will get 15 packs from the expansions in 2018. That's 5 packs each from The Witchwood, The Boomsday Project and Rastakhan's Rumble. That's more value and generosity than Blizzard usually willingly gives. The Bundle goes off the shop on May 2.
These expansions are from the "Year of the Raven", the last Standard year in Hearthstone's yearly cycle. The Rise of Shadows release marked the "Year of the Dragon" rotating out the sets from 2017's expansions. The expansions from 2018's Year of the Raven will still be around for one more year.
The Year of the Dragon rotation was quite different from other Standard rotations. Blizzard sends Classic Cards deemed too powerful and played too often to the "Hall of Fame". This time around, they also sent two cards from The Witchwood expansion to the Hall of Fame.
Genn Greymane and Baku Mooneater, known for the "odd" and "even" decks which manipulate your hero power, was rotated into Wild. It was a sensible move because it limited design space for future expansions. But players in Wild often raise concerns which Blizzard doesn't seem to be listening to.
There are many meta decks which are being played in Standard that need some powerful cards from the Year of the Raven expansions. If you missed getting cards from these expansions it could be worth getting this cheap bundle. If you don't open many Legendaries/Epics, you get some free dust at least.
You can also get free packs by participating in the HCT championships by choosing a champion and spectating the tournament.