Fans of RPGs or turn based strategy games will be equally enthralled. Fans of both will be amazed.
Gamplay is presented as a series of turn-based battles. These are somewhat varied but realistically most are beaten just by killing as many enemies as you can, whether the goal is to kill all enemies, defeat a boss or simply survive a number of turns. The turn based gameplay is compelling on its own but the player's preparation is where the real depth of gameplay is. There are dozens of playable character all w/ customizable weapons and upgrade paths. Certain characters work well on certain maps and against certain enemies and others naturally do not. Really, the means by which you can customize your party is pretty much staggering and it will take multiple playthroughs to explore all options. All of these options can make the Sacred Stones sound a bit obtuse on paper but actual gameplay is intuitive and simple. That developer Intelligent Designs managed to layer such depth on a simple design is a real accomplishment.
The Sacred Stones is set on the continent of Magvel which, if you are not well versed in geography, is fictional. There are six nations on Magvel who have long lived at peace, protected from evil by the titular sacred stones. Of course, since peacetime doesn't make for much of a game, one nation rebels against the established order and seeks to destroy the sacred stones and it is your task to stop them. A simple excuse plot would be perfectly adequate for the kind of game The Sacred Stones is but this is much deeper an more poignant.
What really gets the gamer invested in the game though is not the story but the fact that your characters die permanently. I was personally anxious about this dynamic before playing but it really does serve a purpose, which is to make you be more careful and precise w/ your strategy. Most of the time, it is not worth it to lose a leveled up character in order to beat a tough battle so it forces you to pace yourself and try different things in order to find the best way to win. Despite this, you do have a whole stable of extra characters you pick up along the way and ways to level them up outside the main story so it is pretty difficult to find your game save in an unwinnable state such that you have to restart from the beginning--though that can happen. Overall, the dynamic pushes you to avoid sloppy play and if you do happen to lose a few characters on the way, gives you a reason to try again once it's all finished.
And that is really what's great about Fire Emblem: The Sacred Stones. Many RPG's increase playtime by including a whole bunch of sidequests and secondary goals. The Sacred Stones is just so good you'll want to play it again.