The Groggy Ring game was 100% true to the manga though, and probably the best animated action of the whole series. Episode 211 was amazing!
The Donuts Race changed a bit but was fun nevertheless. Instead of just having Usopp+Robin+Nami v Porsche+Monda+Fishdude, there were many other boats taking part in the race : Zoro+Chopper, Luffy+Sanji, and several boats with Foxy's henchmen. But it was all additionnal fun and in the end, the duel between the two main boats was more or less faithful to the manga.
They added several games so that when Luffy and Foxy had to fight, both Chopper and Robin were part of Foxy's crew. Impossible to win both in one game, so they included a plot device : the last game's winner would take 50 people from the other crew. Since the Straw Hats didn't have that many members, Foxy claimed their children would be his too, which had a funny scene with Sanji thinking about having a daughter looking like Nami.
The last fight was again very faithful to the manga, but everything that happened past it was changed. First, since Luffy won, he claimed both Chopper and Robin back, plus 48 members of the Foxy crew - all but Foxy, Porsche and Hamburg. Then, he dismissed all of them. Because the animators wanted to include a filler arc, they couldn't immediately show Ao Kiji, as it would be strange to see Robin shocked, then all of the sudden happy again in a filler arc, then again moody in Water Seven. So, they postponed Ao Kiji and created another ending for Tonjit.
Then came the filler arc, then two episodes featuring Foxy, Porsche and Hamburg plotting against the Straw Hats and getting their crew back from the Frog Captain (the guy Foxy won through the suggested DBF preceding the one vs the Straw Hats in the manga)… and finally, they landed on a deserted forest island with Ao Kiji and some lost people. Instead of helping Tonjit, Ao Kiji helped those lost people.
So, yeah, they screwed up the DBF arc a little, though the three main events were perfect IMO... but we should be thankful as it is thanks to these fillers that we now have a filler-free Water Seven.