This JRPG style game isn't bad but it's held back by several flaws.
THE GOOD : the voice acting for the main characters, especially Maya is outstanding. The spell cards are fun to combine and the graphics for the time are pretty good. The character models aren't the best but I did like the backgrounds and lighting effects. What music is there is good although there's mainly over world and battle themes. Dungeons are generally silent. Sound effects are pretty good as well and satisfying to hear. The story isn't bad either. Sometimes you have to bring a certain character to an NPC to get them to say something specific or get a key item. Think about which character might be useful with a certain NPC or on what shell. Your battle attack/spells have 3 levels of power leading to some strategy involved. Enemies can potentially be bypassed as in games like Earthbound and Chrono Trigger and there are no random battles, enemies are on screen almost always.
THE BAD: The dungeons get monotonous really fast, mainly because it's mostly about flipping switches to open doors that often lead to more switches. You're either opening doors or making new pathways and at the end you find a key item or fight a boss. Then you have to usually backtrack out of the dungeon manually which can get annoying if you just want to get out of there and don't care about exp and gold. An option to teleport out would have been helpful. There's also a lot of backtracking, and clues to what needs to be done next can sometimes be confusing to figure out. Again, bringing the right character along on the right shell can be a big help in this aspect.
Another major glaring problem for me was the slow animations during battle and the sound effects often took even longer, still playing even when the animations were done. This is especially a problem with the zombie enemies. I found myself using machine gun characters when I could, just because their attacks are faster.
Characters take one turn at a time or combine turns during spells. You can't input commands usually until the character is done with their attack or spell/item usage unlike say a Final Fantasy game. This stuff is a bigger problem during the first half of the game, once you get a spell card that lets you attack all enemies it helps cut down on this some, but it's still a problem. I found myself running away from battles towards the end, just to get to the end of the game.
Overall I enjoyed Septerra Core for the voice acting and story/setting. The battle system isn't BAD as an idea, and the card concept is neat, it's just feels slow as heck, at least for me. The switch flipping and backtracking got on my nerves fast. If the battle system was just faster, I might not have minded the rest, because that's mainly what made the dungeons more of a chore than anything else. If you're the patient type you might find the battles less grating than I did.
I got it on sale here for a buck so it was worth the price. I'd give Septerra Core a 7/10. I'm going to overall recommend the game. Just be aware of the issues above if you decide to play.