The Beach is about paradise, what we'll do for it and the consequences. Nothing is perfect, everything has a cost.
The good. Intensely dramatic scenes. A modern phantasmagoric mix. Superbly paced scenario with great cohesion and editing. Solid characters, very realistic actions and reactions. Nice score. Superb acting.
The actors. I'll just mention the two best ones: Leonardo DiCaprio and Robert Carlyle.
The bad. That video game overlay. It's not necessarily a faux pas, because it's well tailored to the persona and his psychosis, but it just doesn't fit very nicely with the rest of the movie style.
The ugly. Nothing.
The result. A must see. Sensible souls should avoid for the drama, and a very gory scene.