Cult classic and probably the best Genesis game EVER.
I remember buying this game wihtout having heard that much about it, reading the manual on the way home and thinking "hey, this sounds cool". Then I put the cartridge in, the intro scene came up and I was hooked. I had honestly never seen anything like this game before, graphics or gameplay-wise. It is a top-down action RPG with a heavy emphasis on the action part.
The game starts when the main character Ali finds a golden bracelet. The bracelet informs him that there's another (silver) bracelet out there and that it's also awakened, so it'll be good vs evil all over again. The bad guy happens to command a huge army of ogres and rats, but Ali can recruit several elemental spirits to help him in his quest. There are a few plot twists that are nothing new, but the characters are well designed enough to make you hate the bad guy by the end of the story. The interesting part is in the gameplay.
Which is great. It's basically the Zelda formula we all know and love with a few twists. For starters, Ali is far more agile than Link, and a much better fighter. The fighting system, in fact, is an adaptation of the one in Streets of Rage to make it work in an overhead view instead of a side scroller. That means Ali's moves go far beyond holding a button to do a spin attack. You can jump, duck, do a Chun-Li-like multi-kick attack, dash and overall fight like a tasmanian devil on ecstasy. Ali can also level up, which makes him stronger, and acquire other weapons besides his trademark dagger, though they break after a few uses. If anything, Ali is too good of a fighter. Zelda games aren't too hard to beat and you don't get killed a lot, but if you stop to kill every monster you come across in this game, Ali will have god-like powers by the time you're halfway through the game, to the point where you won't get to use the more advanced combos because no normal enemy can survive past the first few hits.
And then there's the spirits. You get one after each dungeon in the game and you can only have one active at the same time. When active, the spirits will appear onscreen and do their thing (fight enemies, heal you, protect you from harm or grant access to new areas), while slowly draining your mana just by being there or by using their special moves. They all look cool and feel useful, but the best part about them is that you have to summon them by throwing a light sphere at some element in the environment that relates to them. You need water to summon Dytto, the water fairy, or fire to get Iffrit out. This sets up the game's puzzles, but also creates a whole new strategic layer in the game, where you have to balance mana drain from having a spirit active and into the world with the possibility that sending him away might leave you stuck somewhere with an obstacle and no spirit to go around it without having to backtrack. Again, the only problem with the system is that it gets too easy after a while if you level up your character enough. Level design is great, with lots of hidden areas, puzzles and challenges. In this, however, the game falls a bit short of Zelda's gold standard. While the puzzles aren't stupid or pedestrian in any way, they're not as complex or brilliant as we're used to see in Zeldas. Still, they do the job just fine and put the great controls to good use. Exploration is similarly rewarding, with hidden treasure and an open world to discover. Here, again, the challenge is somewhat diminished by a little flag that appears in your map to tell you where to go next. It feels slightly cheap and it's there to counter the fact that this game has far less NPC's and dialogue to get you from point A to point B than, again, Zelda, but it's hardly a deal breaker.
All in all, this game is a true classic. It's a great game on its own right, the best action RPG ever on the Genesis and the best Zelda that's not a Zelda (much, much better than the whole Mana series, for instance). If you're done with Ocarina of Time, and A Link to the Past on the VC, this is the next logical step, and it's worth every minute of your time.
Two minor details from outside the game: first, it's called The Story of Thor here in Europe... which makes no sense, because there's no Thor in the game. No spirit is called Thor, the main character is called Ali and if one of the battling bracelet gods mentioned in the beginning of the game is called Thor, nobody cared or noticed.
Second, there was a sequel to this game in the Sega Saturn. It was awful. It killed what could have been a great saga (a bit like the Shinning Force Saturn games ended that one). Avoid that other one at all costs, it will only erase your sweet memories from this one (not that you canf ind a copy of Story of Thor 2 anywhere at this point, though).