All the fun of a CCG like Magic: The Gathering without having to buy or deal with cards or the insanely complex rules.
The game also now runs very well on modern Windows OS versions (I'm running it on Windows 7 64-bit) where previous versions had some issues.
The game is basically Magic: The Gathering (in fact it was designed by Richard Garfield, the original designer of Magic) with a simplified rule set and no need for "land" to get mana resources.
While there are multiple play modes (single duel, a single player campaign, and local and online multiplayer among others) I will describe a basic single player duel.
Each player's "deck" consists of four cards from each of five different "elements" (like colors in Magic) for a total of 25 cards available to you in any one duel. The first four are always Fire, Water, Air, and Earth, and the fifth one will be chosen from the twelve other sets included in the current version of the game. You can chose which you want or let the game pick one randomly.
The four cards you get for each element are chosen semi-randomly out of the 8-12 cards that exist in that element type, so each game will be quite different even if you choose the same fifth element every time.
There is a "power" level for each element, which serves as mana and is the currency used to pay for cards when they're played. So you have five mana pools, one for each element. Normally, all five are increased by one at the start of your turn (though there are cards which can increase or decrease this, etc.) At the start of a duel you get a certain number of power points distributed semi-randomly across your five elements, so again each game will start a bit differently. You might start with three points in Air one game and one for Water, and that might be reversed the next game etc.
Each person has six slots for creatures which oppose each other, so each of your creature slots has an opposing slot which, if occupied, will block that creature's attacks.
Each player starts with some amount of life (typically 60) and like Magic the goal is to reduce your opponent's life to zero (or less). The play is basically a lot like Magic. You play creatures and spells, creatures have attack and defense, and if you've played Magic you pretty much know all the mechanics here.
But things are a lot simpler in this game. Each turn starts with your power going up by one for each element. You can then play one and only one card which is either a creature summon or something like an instant spell (deal 25 damage to all creatures, heal caster, etc.) Each card has a power cost that must be paid from the power pool for it's element. All of your 25 cards are available to play every turn (if you have the power level to afford them) and you can use the same card as many times as you like in a game. So there's no randomness or "draw" process hence no frustration for not getting the cards you want when you want them. All the cards in your "deck" are effectively always in your hand.
Once you've played your one card, all your creatures will attack and will be blocked if their opposing slot is occupied. There's nothing like flying or optional blocking. After combat is resolved your turn is over. That's it. There are no interrupts or other exotic game mechanics. The turn sequence it trivially simple (one card + attack) but there is still plenty of variety and complexity to the play.
You can buy the game direct from the web site or through Steam and one or two other channels, but I think buying direct from their web site is probably the best option. You get an activation code which allows some number of activations of the game. So far this has not seemed to be particularly limiting.
Overall this is just a great casual game for anyone who finds the play of games like Magic: The Gathering appealing and especially those who want a simpler (and better thought out) experience with no need to deal with the expense and whatnot that go with physical cards.
This is a great casual game. You can play a random duel in just a few minutes. Easily worth the $20, or $10 to upgrade from a previous version.
This review is of version 1.21