The mishnah states that one must understand Ezekiel's description from one's own knowledge. This appears to be something of a code phrase and occurs only here in all of rabbinic literature. At any rate, it appears that one should study these deep mystical matters either by oneself or, at most, with one other person of like understanding. Rabbi Akiba departed unhurt. Let's deal with what happened to each sage in turn.
Fine marble can give the appearance of water.
According to B. Baba Batra 4a, the steps of the Temple looked like water even though they were made of marble. Rabbi Akiba was perhaps warning his friends that they were entering the Temple and not to be confused by its other-worldly appearance or by the magnificent things they saw there. Ben Azzai saw a mystical vision, perhaps Ezekiel's, and immediately died. Perhaps he was so swept up in the heavenly sphere that he wanted to become all soul and abandoned his body so that he could become completely soul and experience the wonders of the mystical realms. Ben Zoma looked at the mystic wonders and was able to maintain his physical life but his intellectual and spiritual lives were consumed by what he had seen.