It's not a bad game if you like blending a card game and RTS. Similar to Magic The Gathering there are various Elemental nodes around the map, and you have to control them to power your cards. Some cards might need 4 of a specific type, some might need 2 specific and 2 any, and the basics just need 1 or 2 total. It's a pretty intuitive system. The PvE aspect was pretty fleshed out, last I played (before it went free-to-play, so it's been a while), and some maps require co-op play. They're generally split into Solo, few people, lots of people maps. Completing these on various difficult awards you card upgrades.
However, when I played the base "decks" were pretty slim, and especially if you want to get into PvP, I imagine you wouldn't be competitive without buying new cards.