You certainly noticed it, but the recent changes Hearthstone underwent made Ranked Rewards much more interesting for the vast majority of players.
Previously, the chest obtained at the end of a season was pretty disappointing: a Legend player was rewarded with a card back, a golden epic card, and three golden rare cards.
Now, you'll obtain at least one pack of the latest expansion plus a rare card starting from rank Silver 10.
If you manage to reach Platinum 5, your chest will contain three packs and five rare cards, for a total of 20 cards. Moreover, since you can't obtain more than two exemplars of cards you already possess — unless you already have all of them for a specific class 1 these new rewards will offer you new cards almost all the time.
Keep in mind that "First-Time Rewards" only apply once per account, and not once a month.
Original content by Jean-Vincent "Durvil" Cannata.