If you are hoping for action packed sequences like what happen in an Avengers movie, then you are not going to find them in this book. That doesn't mean there are not exciting and tense parts though. The action is focused squarely on man vs nature in this Verne book. Additionally, some of the most tense parts for me are more cerebral than action packed.
For example, when the group begins their journey toward the center of the earth, they are descending down through the throat of a volcano. The volcano is supposedly extinct, and that should create less anxiety, but be honest, would you want to descend through earth's crust through a volcano?
The underground storm sequence is fairly action packed too I think. What's great about that part is how Verne builds up to it. Verne lays down so much anticipation to the impending storm that the reader can't help but feel excited and apprehensive about what's coming.
‘We’re going to have a storm,’ I continue, pointing towards the horizon. ‘These clouds are lowering upon the sea, as if to crush it.’
Once the storm hits, it's not some quick rain storm that's over in a few hours. It lasts for days. The narrator's description of the storm is vivid, exciting, and action packed.
The mass of water vapour becomes incandescent; the hailstones striking the metal of our tools and firearms become luminous; each of the waves surging up resembles a fire-breathing breast, in which seethes an internal radiance, with each peak surmounted by plumes of flames.
There's lots of exciting action stuff after the storm too. Explosives, earthquakes, and surviving the volcanic eruption that spits them out.