>>32152566Explorers changed it the most in that Rescue Team doesn't really have much of an overarching plot. Most it consists of small sidequests that don't exactly connect, besides a few characters being reused in some of them, and it's only until the protagonist gets kicked out of town when the natural disasters plot starts to show up.
Even then, Explorers still shares a bunch of concepts that Rescue Team has, too. Characters like Caterpie and Metapod are reworked into Marill and Azurill, the game starts off rather lighthearted until later on in the game, when they get wrapped up in a serious threat. In Rescue Team's case, this threat was the recurring natural disasters caused by a human-turned-Pokemon, and in Explorers' case, the threat is time coming to a stop, and the two are similar even from a gameplay standpoint since it forces players to leave all their allies behind besides the main duo, and do a marathon of dungeons with the only grind points being side paths. Team Skull and Meanies are also similar, a group of bullies with the leader having a change of heart in the end. The climax of the games are also similar in that they're secluded places that only a few key characters know about, and both end in the protagonist having to climb a tall tower to put a legendary Pokemon back to its senses. Both games also share the series-wide plot points I mentioned before, too, like the amnesiac protagonist that has to leave in the end.
They're more similar than you think.