Its really far from a card game. Put it like this, you collect skills which are considered "cards" that you use to fight with. You can only have 30 cards in a arsenal which is considered your "deck". Before you begin a fight, you can pick 4 skills(cards) out of your arsenal(deck) and map them to the face bottons of the controller.
The stratergy element comes into play with how you select and use your 4 skills to fight with. You can be a defensive, long ranged attacker or a aggressive, closed ranged attacker depending on how you picked your 4 skills.
For instance, lets say you have selected to fight with:
Fireball 1= A button
Ice 1= X Button
Levitate 1= Y button
Block 1 = B Button
When fighting, you can move your character around as if it were a first person shooter or a 3rd person shooter. You have to pull the right trigger to select your target and depending on how far away he is, the target reticule will change colors.
If you know your skills, you would know that "Fireball 1" is a long ranged attack. So when you press the "A" button, you throw a fireball at your target. If it connects, he loses health but he can also block the fireball or reflect it back at you depending if he has those skills.
Now after you used the fireball, you lose 5 Aura points. Aura points are like Mana/Magic points you find in any typical RPG. You start the game off Level 0 with 20 health points and 5 Aura points. So after I used the fireball, I lost all of my Aura points. But the Aura points regenerate automatically. So in about 2-3 seconds, I'll regain my Aura points back and I can use my skill again. Of course, if you have no Aura points, you cannot use a skill. Each skill takes a certain amount of Aura points so it is recommended that you dont pick all 4 skills that drain your Aura quickly. Just another element of stratergy you must consider before you begin the fight.
Now lets say I connected with my Fireball 1 and hit my target. Since I have no Aura left, I'm on the defensive end. My opponent also throws a Fireball 1 at me. The Fireball 1 skill moves in a straight line towards the target so it is easy to dodge. So I can ethier manually dodge the fireball(just moving right out of the way) or I can jump over the fireball(with the jump button) or I can use my "Block 1" skill and block the fireball or I can use my "Levitate 1" skill to fly wayyyy over the fireball and miss it completely.
Lets say I used my "Block 1" skill and blocked the fireball. Depending on my opponent, he can ethier run and hide to recharge his Aura or if he has more Aura left, he can throw another fireball at me. My Block 1 skill only used up 1 Aura point so I can pretty much block anytime I want since your Aura recharges automatically. I would say that it takes 3 seconds to recharge 5 points so you can do the math and see how that happens.
The battles can be good cause the eviorment is totally desructible. You even have skills that you can use to throw huge pieces of concrete or knock down a part of the scene onto your opponent. There is tons and tons of diffrent stratergy involved for advanced players. I can already see. If you noticed, this sounds nothing like a card game after all. Only card based elements is the fact that you have to collect skills. Just like Pokemon Balls(Gotta catch em all!!) And you can only build up a deck of 30 skills but you can have many diffrent arsenals(decks) you can use in any battle.
Now as for the offline missions, you hit the nail on the head. They are there to only make you character better. You start off in this underground world and you run into NPCs who basically send you from person to person to do missions for them. The first missions consisted of just destroying some random practice enemy. Later missions involve rescuing ppl and fighting mulitple enemys at once. Nothing special but just fighting in this game is addictive. You'll quickly realize that the 100 missions they advertise on the back of the box are simply: Talk to person A to recieve mission, complete mission, then person A sends you to person B to do another mission. Wash, rinse and repeat.
But so far, the story has been pretty good suprisingly. The game starts with a 5-10 minute FMV cut scene which descibes the story. Its not bad at all considering that you really did'nt need a story with this game. The meat and potatoes lies in multiplayer and Xbox Live. BUT...and this is a huge BUT, you HAVE TO START THE OFFLINE SINGLE PLAYER IN ORDER TO OBTAIN SKILLS TO USE IN MULTIPLAYER. And the bad part is, the game starts off pretty slow. If you expect to rip the cover off and hop right online or plug a extra controller up, you're in for a suprise. The point of the missions is to get money to buy skills or you can earn skills and you can ethier buy skills at the offline shop or go online and trade with other ppl. And I'm sure they probably sell skills also. But I have'nt tried online yet so I cant really speak for it yet.
OK, to finish this off, I gotta say that this game really is a sleeper hit. I'm sure the words "card game" may scare some away but its far from it. Think Magic: the Gathering card collecting and instead of just flipping over cards, you actually play you cards out in bueatiful animations that can cause all sorts of carnage on a level. The feeling you get when you smash a fireball at a opponent who was flying threw the air and watching him fly 100 yards and through the wall of a building, while the rubble of the wall he smashed though falls on top of him is priceless.