From today Rocket League is Free to Play and to help promote Rocket League and Epic Game Store, if you get it free on Epic they will add a USD$10 voucher to your account. In Australia this was an AUD$15 voucher as it automatically determines local currency.
I would describe the gameplay as Soccer with acrobatic cars. As a previous fully pay to play game, going free to play may be a sign that player numbers were dropping off.
It is a good time to get on to Epic Game Store because they are giving free games every week with some great older titles, currently Watch Dogs 2. But previously Borderlands 2, HITMAN, Civilization VI and Grand Theft Auto V.