To make an action scene work, you must not only detail what the characters are doing with their bodies and weapons, you must also include the viewpoint character's emotions and senses.
Adding emotion isn't an either/or situation. It's just as vital to add emotional layers to the physical action as it is to have brief moments of introspection when the battle isn't going on.
Characterization isn't just introspection. It's characters interacting with each other and revealing themselves in bits and pieces.
Your band of adventurers may not sit around "sharing their feelings" in touchie-feelie moments like a Dr. Phil show, but they've been around each other enough to know that one hates the bad guys because they murdered his wife and kids, and he's liable to attack without thought and ruin their surprise attack.
He may be clutching the sword at his side, his other hand opening and closing in nervous energy, and another adventurer may warn him to relax and may mention the wife and kiddies.
The image of his wife's raped and brutalized body could flash through his mind, and he fights his raw anger and lust to kill. That won't slow the action down like having a long interior flashback of him finding his family's bodies, and his vow of revenge.
Instead, it adds to the excitement of the coming action because the reader now questions whether this guy will lose his cool and get everyone killed.
An even better way to present this information is to put it in an earlier scene that isn't action intensive so the reader will know the details and will only need a slight reminder of this character's motivation and tendency to attack without thought.
After some rewriting, if you still aren't happy with the emotional content of your story, you may want to look at the central story idea. Do your characters have a real emotional reason to be doing what they are doing?
Their hunt for the lost treasure should be as much about their emotional reason for needing the treasure as it is about simple greed. That emotional reason should be important enough to make the reader want them to succeed as much as they do.
Maybe the main character is after a magical sword which is the only weapon which will kill the dragon currently ravaging his homeland, and he doesn't really care about other treasure and the life of drunken decadence and dancing girls it promises the other characters.
Maybe the other characters have laughed at him, but they've admired him and gradually they have been drawn into his quest for the sword, and in the end, they'll choose to get the sword with him and lose the other treasure.
Maybe the one who laughed the hardest and made the main character's life hell along the journey will be the one to sacrifice himself so that the hero can rescue a homeland the scoffer has never had, but now wishes to have with his whole heart.
If you make your character emotionally invested in each action scene, and make your reader emotionally invested in your story, you’ll have a story no one will put down.