Having recently watch the newest episodes of the anime in dub, i use this as a reference. One piece is a faithful adaptation with a few minor changes.
The main character Luffy at times feels more like Captain Jack Sparrow than the Luffy we know from the anime. Nami is supposed to be on the same Ship as Luffy and Koby instead stealing a different ship. Nami has a fight scene with an extendable bow staff when it is something she receives from Usopp only much later on in the anime series. She also does not fight alongside the straw hats until receiving the weather baton. Zoro never cuts Helmeppos hair. Koby never punches Luffy, instead he punches Helmeppo in the Live Action. Buggy the Clown seems more like a modern-day Joker from Batman Comics than Buggy the Clown from the anime. Also Luffy and Zoro never set out on their two man boat, instead they use the ship Nami stole earlier in the episode.
The rest of the scenes do remain pretty faithful to the original show. The fight scenes are entertaining and dynamic, while the characters feel alive and enjoying the world around them. The characters seem like a mix of themselves pre and post TimeSkip of the anime as if they had already been an established team.
For new and old fans,I would highly recommend this series.