I have AMD Radeon HD 7600M 2GB dedicated and shared up to 3.8GB VRAM.
Highest display setting still give me 57-60FPS without a single FPS drop even with tons of people and skill effects at a time. Very lightweight.

As promised, the story begins with Luffy met Zoro and continues until Dressrosa arc. But Dressrosa arc is original game story, different than original story from manga and anime.

There are 37 playable characters, and 27 NPC which can only assist you. Total 64 characters.
The battle system is more fun than Dynasty Warrior 6 (the only musou game I played). There is Kizuna Attack, Kizuna Gauge, Kizuna Rush, and Special Kizuna Attack. By using all of them, I can get at least 2000 kills every round.
It's so fun to wipe all enemies on the screen with Special Kizuna Attack.

And there is a fun thing if you use Sanji, you can't attack woman directly. Sanji will be knocked back instead. The game will warn you if you select Sanji and there is at least 1 woman as enemy. LOL

Eventhough Steam tags this game as Partial Controller Support, I use Xbox 360 controller all the time and never used keyboard/mouse at all.

Some rant :

• For 100% achievements, it will take more than a hundred hours gameplay time, and you have to play Dream Log mode over and over again to complete the gallery achievement, because you need to maxed all characters crew level (level 5) including 27 NPC which can't be played. Those NPC appears in some islands, but most of the time they only appear by chance.
  It is very repetitive gameplay to unlock 100% achievements.
  
• The control setup for battle doesn't tell which button for what. I was confused at first when looking at combo list. But it didn't take me long to figure it out.
  
• The game doesn't support my laptop resolution (1366x768) so I have to play it at 1280x720. This makes steam overlay zoomed in and looks a bit blurry.

Overall rating : 8/10