I definitely do not regret my decision to buy this game.
I bought it a year ago as a present and we played it like 4-5 times, but it was loads of fun every time. We would play more often if it didn't require so much preparation (sliced fruits, whipped cream, alcohol, sexy outfit.... shower (lol, just kidding =D ) ).
Some cards are so-so, but some are very interesting, give you some new ideas and really turn you on for the final part of the game.
So, don't hesitate, give it a try, you are definitely going to have a romantic evening (at least) and it's totally worth 18 pounds.
Also it's not a one-time-game, you can play it many times - by the time you'll be done with all the cards you are gonna forget what was in the beginning, so you can start all over again =). As I said, we played like 4-5 times and we still have some cards we haven't seen yet.
Oh, after writing this review I feel like playing again =) I think I'm gonna arrange another Monogamy-evening this weekend.