Traditionally the 3rd album from a band is regarded as the most difficult (Oasis - Be Here Now/Coldplay - X&Y) and Plastic Beach does indeed suffer following on from Gorillazs superb debut album and follow up Demon Days.
To be fair Plastic Beech is a great album with several stand out songs. Stylo is a great pop single, On Melancholy Hill has an addictive beat and Superfast Jellyfish is another favourite of mine.
Plastic Beach is probably the most 'pop' sounding album Gorillaz have produced so far. Its very easy to listen too and features some interesting cameos from Snoop Dogg, Mos Def, Lou Reed and Bobby Womack.
Its not far from being as good as its predecessors, in fact you argue its more easily accessible but it does feel slightly bogged down in the middle with some lumbering tracks.
Plastic Beach is a very good album with some great pop songs but it is still the difficult third album and arguably not quite as good as the first two. But considering the quality of those how could it ever live up to expectations?