The plot is pointless. It covers generic ground and in a way that suggests that it doesn't really care. It's all in service of the songs. Any excuse to break out into a routine (the film bends over backward for them). Which some people may enjoy, but it makes everything seem irrelevant. If the plot isn't going to do anything and the film believes the only real draw is the music, why not just listen to the tunes by themselves (there is a playlist on YouTube)? Hey, with the price on cinema tickets these days, it might be cheaper to get the music and head to Italy yourself.
Still, I guess people like musicals like this where pre-existing songs are worked into some form of narrative. I find that they aren't the most interesting things, but I at least managed to find this a bit more engaging (not as boring) than something like 'Rock of Ages', though it did struggle to keep my attention (it got me to go off on a trail of thought that ended with Spielberg's 'Munich'*). And this does try to keep things bright and is harmless overall. So it wasn't some despicable monstrosity. More a pointless exercise in whatever it was meant to be (I can only assume it exists as counter-programming for the FIFA World Cup).
*I think the trail of thought went like this (should you wish to know): They're in sunny Italy on a beach, so I think Mediterranean. When I think Mediterranean, I tend to think of the Eastern region - so countries like Cyprus, Turkey, Syria, Lebanon, etc - and I started thinking about Cyprus. For whatever reason, I started to think about films set in Cyprus and recalled that hotel bombing scene in 'Munich' (the bit where a couple on holiday are collateral damage). And there you go. A pointless recollection.