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Gen 1-4: Old Pokemon
Traditional style maps with horizontal and vertical routes and at least some backtracking through places you've been. Classic fixed exp rewards. Exp share is a held item, or key in gen 1, and preserves the same quantity of exp but just redistributes it. Less handholding/tutorials unless you seek them out.
Gen 5-7: Modern Pokemon
"Subway spider" style maps with diagonal routes, optimized for pretty much zero backtracking. Exp scales with your level relative to what you beat. Exp share returns to more like its gen 1 "exp all" functionality but increases the total exp now. More forced tutorials.
Geb 8+: Nu Pokemon
Dexit. Gradual move to open world with paths on the ground but no marked routes. Prevents or discourages the player from going into areas that are supposed to be for later by putting landscape elements in the way or putting higher level pokes. Same scaled exp, but exp share is always on. Also less content and more glitches, but this started around 6 and became blatantly obvious in 8.
