Like Dominion, Thunderstone has something of the feel of a trading card game (TCG), but is a complete boxed set, with no 'trading' or booster packs required. However this is not a mere clone, but a better version.
The story is that the “... Thunderstone has been discovered in the Dungeons of Grimhold and the Doom Knights have sent their minions to claim the relic. The Villagers of Barrowsdale gather brave souls to face the dungeon and keep the Thunderstone out of the hands of the Doom Knights.” The reason I bother telling you the story is because the story is meaningful and adds to the experience of the game. You recruit a party of heroes and equip them to delve the dungeons in search of the Thunderstone, which is guarded by hoards of unspeakable evil. Designer Mike Elliot took the get-money-to-get-victory-points game of Dominion and added some kickin' flavor.
The metagame of deck building found in TCGs is the core gameplay of Thunderstone (and Dominion). The gameplay remains the same as in Dominion -- draw from your own deck, play cards, and buy cards to add to your deck. Since there is only room for one band of heroes in this town, the player who can best build a deck that constantly replenishes a powerful combination of cards will be faster and hit harder than the competition. There is little luck in the game since you choose what cards go in the deck that you draw from. If you keep getting a lousy hand of cards, blame the the deck builder -- you.
What makes Thunderstone stand out is that you have two choices: go town recruiting and equipping or delve into the dungeons. You need to recruit warriors, wizards, thieves, clerics, and others, and you have to buy weapons and tools to for the heroes as well. However if you spend all your time equipping and recruiting you cannot defeat monsters, which grant you victory points. Thus you must balance between spending time in the town and the dungeon.
On your turn you draw six cards from your deck and play them. The cards can be heroes, equipment, spells, tools, or monsters that you defeated previously. The monster have victory point values but they also may add gold or powers to the player. Cards either have one or a combination of combat values, gold, special powers. You fight monsters until the Thunderstone is acquired and scoring ensues. The player with the most victory points, usually the one who defeated the most monsters, is victorious.
Thunderstone comes with multiple sets of heroes, items, and monsters cards, and since you only use a few randomly selected sets, each game and strategy is different. If you enjoy Magic The Gathering or other TCGs, but do not want to spend heaps of time and money on collecting and building decks, give Thunderstone a try.
Strategy wise, you want to build a small but powerful deck. Get cards that give you power to destroy weak cards to ensure that you get a constant flow of powerful cards in your hand.