I watched up to the first DP season, where I stopped because I thought the new theme song and the episodes were boring. A few issues I had with the anime:
-Some type immunities are contradicted. Early on it's established Electric doesn't work against Ground, but near the Pokemon League at the end of season 1 Pikachu took out a trainer's Marowak with Thundershock. Also the "aim for the horn" thing. The sprinkler scene in Brock's gym makes sense, but in some other cases (like the Marowak) there's nothing on the field that would change type matchups.
-Ash using the Pokedex to look up Pokemon that he's already seen and used the Pokedex on before
-Some minor errors, like Brock calling Furret a Ground type and "Arbok evolves into Seviper"
-It seems like almost everyone's skill level is completely random. The only ones whose power seemed to consistently stand out compared to everyone else are the Elite Four and Brandon. Ash took three tries to beat Brandon, and eventually won. Then when they went to Sinnoh he somehow lost to Roark's Cranidos, then beat him after Roark's Cranidos evolved.
On a positive note I did like how the anime did Contests.
Also the Bill's lighthouse episode made me legitimately mad/sad because after all that buildup the giant Dragonite finally comes to meet Bill and Team Rocket kept pelting it with explosives, causing it to go away sad, probably thinking Bill lured it there as a trap. And somehow Bill still thinks it'll come back.