I think this is one of my favourite games of all time.
Mechanics are simple enough that newcomers to the genre will find it easy to pick up, but complex enough to allow many different strategies to be viable.
Veterans will find similarities to genre staples such as Final Fantasy Tactics, so if you loved that game - I am positive you will love this one too as I did. Keep reading for a more detailed description of the mechanics.

In combat you have access to 3 commander units and up to 3 summoned fae units. Commander units are unique characters with their own bits of story and special skills, while summoned fae are manifestations of the main character's mana.
During a unit's turn, it can move, attack an enemy, assist an ally, or wait, which activates its wait skill. Commander units also have reaction skills, which are essentially counter-attacks.
With the exception of some physical-type units, all units have one of the elemental types assigned. Elements determine a unit's assist and wait skills, as well as their strengths and weakness against other elements.
The game also has a (very simple) day of the week system, where every battle or story event advances time by one day.
Each day has an element assigned to it, and units of the corresponding element receive stat boosts during that day.

The battlefields are quite unique and interesting. You can take out enemies by knocking them into water (unless they're aquatic units) or pits. Some maps have (visible, not hidden!) traps on them.
There is also a terrain elevation mechanic - all non-flying units use a jump stat to determine whether they're allowed to move to a tile higher than the one they're currently on. Units with arc attacks also get bonus damage if they're above their target.

You obtain new fae (summoned units) as drops from defeated enemies. Once obtained that unit stays unlocked forever, even if defeated in battle. The game has an impressive roster of different creatures that serve different purposes, allowing you to tailor your strategy to enemies you are facing, and synergy with your commander units.
The game doesn't require you to grind levels, as enemy level scales with your characters. The only real benefit of a higher level is more skill points available for your commander.

Behind the childish facade, the story is quite epic and touches some serious topics.
All the characters have their own unique personalities, although some of them don't get as much development as they deserve. While small, the game world is rather charming and features diverse characters facing different problems (although there is a central arc to the story, which isn't apparent at first).
My only nitpick is that the best ending requires playing out the story arcs of 2 characters in the right order, while deploying them in battle together to trigger their unique story events. Without meta knowledge of the game, most players will definitely miss this on their first playthrough. I had a hunch that these 2 characters are like this, and I still missed one of their events, because I did the missions in the wrong order.

Finally the game offers us New Game+ to replay the story while keeping all of our levels, unlocked fae, scrolls, gems, and crafting materials. You still have to recruit your commanders through the story, but they retain their levels and unlocked weapons. What doesn't carry over is your equipment (bike level, summon capacity, etc.), as the game locks some equipment upgrades behind the story, but all your materials do carry over, so leveling them up again isn't that big of a deal.

I loved this game. Unique, with good art and interesting combat - I'll definitely be replaying this one sometime down the road.