>>43518311>Battle FrontierThe first versions never had full Battle Frontiers - we just had Battle Tower clones, like the Battle Subway. BW2 replaced the Battle Frontier with the PWT, Black Tower/White Treehollow, and included the Battle Subway.
>ContestsReplaced with the (inferior) Musicals. BW2 also added Studios to the mix, giving you two replacements.
Gen V also added a lot of things: reusable HMs, seasons, version-exclusive locations, Hidden Abilities (which revolutionized many old Pokemon), solid postgame, the Dream World, and triple and rotation battles.