The original Thunderstruck slot changed how video slots dealt with free spins bonus features by making multipliers on your wins a standard extra. Along the same lines, the Thunderstruck II slot by Microgaming really broke out the 243-ways format that allows you to get paid with one symbol from each reel no matter what order they're in, and it's a format that they've used a lot in recent years for a reason.
Thunderstruck 2 slot has five reels and three rows. It has coins that range from $0.01 to $0.05 each, and you start with a base bet of 30 coins. You can multiply that up to 10 for a total bet of up to 300 coins. This game has a high volatility, but even though the top jackpot is seemingly small, you have chances to win plenty of much larger prizes.
When you get three or more of the scattered Thor's hammer, you'll get one of four different bonus features. The Valkyrie bonus gives you 10 free spins with a 5x multiplier. If you trigger the feature five times, you'll have access to the Loki bonus which gives 15 free spins with random wilds appearing on the middle reel. After 10 bonus rounds, you can get the Odin bonus which is 20 free spins with random wild multipliers of 2x, 3x or a combined 6x. Finally, trigger the bonus feature 15+ times to get the Thor bonus which gives 25 free spins with a Rolling Reels feature that gives you multipliers as high as 5x.
This multi-feature format was very innovative at the time, and it's the inspiration that a lot of games have based their own features off of in the past several years.