chaosaeon , planeswalkers were introduced in Lorwyn back in 2007. This coincided with an in-universe drop in power level for them; they're more like X-Men style mid-level mutants, rather than all being reality warpers. About their card strengths, a fair amount are released every year, but only a few get much attention, like any other card type. There were always rares that were much more expensive than other rares, and the math works out so that a particular mythic rare isn't that much rarer than a particular old rare. The size of the Magic audience has grown a lot, though, which accounts for the more wild prices.
Since you haven't played since before then, that means you probably also missed these rule changes.
* Mana burn doesn't exist anymore. Unspent mana just disappears, instead of dealing you damage.
* The term "mana pool" isn't used anymore. You just "add G" with Llanowar Elves.
* Combat damage doesn't go on the stack, instead all happening at once in the combat damage step. This means you can't have a creature enter combat with another that would kill it, sacrifice it, and have it still deal damage.
* Terminology changes, like the "in play zone" being the battlefield and the "removed from the game zone" being the exile zone. Creatures die when they're put into the graveyard from the battlefield.
* The legend rule only applies to your side of the board. Both you and your opponent can control the same legendary creature.