If you took a trading card game like Magic: The Gathering, added some board wargame mechanics, and threw in an online player-matching server, you'd have something very much like SpiritWars. As in Magic, you have a hand of spells you can cast, with your hand replenished one card per turn. Some of the spells create power sources; others create defenders who do not move, but can be used to block attacks of enemies nearby on more vulnerable creatures. Still others are units that can move and attack. Rather than having a line of cards facing your opponent, however, the game is played on a hex grid.
To win, you must reach and destroy your opponent's castle. Getting out some fast creatures to scout is a good idea. The net effect is to sustain the metagame of deck construction, in which you're always trying to find the mix of spells that allows you to win, while adding an element of planning and strategy through the boardgame elements that's lacking in pure TCGs.