>>36526546If you already have a 3DS, Ultra Sun/Moon are the latest and most worthwhile to get. The major complaint with them is that there are too many cutscenes/handholding moments. Alola is 4 islands, HMs are replaced by "Poke Ride"
Main things added since Platinum/Soul Silver (Gen 4):
Mega Evolution (Gen 6) - A powered up form gained through a Mega Stone, increases your stats and gives a new ability.
Z-Moves (Gen 7) - Super attacks that require a Z-Crystal to be held, powers up moves of corresponding type. Z-Earthquake becomes a 180 power single target attacked, etc
