Well well well.. I wouldn't have thought the Buckinghams belong to the sunshine pop genre. Although this is of course only what Wikipedia states on the matter. I first started listening to the Buckinghams due to last.fm recommendations. Their music can be described as classic late 60s American pop music and it does sound a lot like sunshine pop. There are definitely baroque pop elements, such as a strong presence of horns.
Musically, the Buckinghams could be placed somewhere between the Four Seasons and the Beatles, with some sunny gentleness added to the mix. The whole concept of one man singing lead and the rest of the guys doing multipart harmonies resembles the Four Seasons concept quite a bit. Carl Giammarese does a great job with the lead vocals. He may not perform with a distinctive falsetto like Frankie Valli but there is a lot of gentleness and bubblegum sound in Giammarese's voice. He also gives nicely rocking performances when needed.
The Buckinghams wanted to identify with the success of British Invasion groups. Therefore they chose a British-sounding name, dressed up in suits and even recorded music from the Beatles (I Call Your Name). They had several hits in the States and their version of Mercy, Mercy, Mercy was the most successful version of the song.
It is cool that the the Buckinghams are still performing and sounding really good. Giammarese and bassist Nick Fortuna were even recently featured on the big Happy Together tours. I can't get enough of their music!