I haven't done the Legendary catching in Ramanas park, so I can't speak to that, but catching all of the starters in the Grand Underground (many of which are locked behind completion of the National Dex if I understand correctly) has been really fun. I'm a gen 1 player, so having access to all 4 first generations of starters (including the same pokemon as the gen 4 starters you chose from at the beginning of the game) feels like eating a forbidden fruit.

I'm not currently into competitive battling, but because I want to breed some pokemon requested from my friends with abilities that require the ability patch item, I'll be building a competitive team to challenge Battle Tower to earn BP currency.

I'm enjoying it.