Yes, the sequel (Viva Blackpool) is bloody awful - but don't let that put you off: Blackpool itself is sensational.
The device of introducing big, corny song-and-dance numbers into drama-comedies was first introduced by Dennis Potter in Pennies from Heaven and The Singing Detective. Here the device works excellently. You can't walk through Blackpool without hearing music playing somewhere in the background, so why not?
This is an accomplished comedy-thriller, but the comedy never detracts from the thrills and nor do the thrills spoil the comedy. The BBC tried something similar with Funland, also set in Blackpool, some time later and it didn't really work. Here it is pitched perfectly: you care about the characters and you know that Ripley Holden is a tragic hero of positively Shakespearean proportions.
Brilliant from start to finish.