>>38244132Blue/Red Rescue and Explorers of Sky both can be jumped right into, they're virtually identical gameplay-wise.
You start with a main character and your partner that you choose at the very start. If your partner dies, you also die.
The rest of your team you can recruit randomly after killing them. In Blue/Red you have to have their 'friend area' which is a location you can buy that allows you to recruit certain Pokemon. For example, owning 'Tadpole Pond' let's you recruit the Poliwag line, the Lotad line and the Surskit line.
They sound pretty dumb on paper but they've all got a comfy as fuck design, their own soundtrack, you can just wander around in them and see your recruits living in their natural habitat. I wish they'd come back desu. In Explorers you just talk to an NPC to change your team, no Friend Areas required.
Unfortunately most story missions (especially in Explorers) are player+partner only so your recruits become underlevelled really quickly and aren't all that useful until you have a chance to use them in the post-game.
Evolution is locked until the post-game in Red/Blue, and the post-post-game in Explorers. But as someone else said, evolution really doesn't do anything besides aesthetics.
