As an old boomer guy I'm not really in the demographic for this movie, and I put it on for background noise while doing something else. I didn't expect it to begin with people battling zombies in a shopping mall! (OK, not real zombies, but still...) I ended up giving the movie 90% attention throughout, instead of the 15% I'd originally planned. It has an endearing main character, some delightfully quirky bits (the zombies, the crab and puffer fish, lawnchair man,...), and a plot which was totally predictable but still left open some questions about how it was going to unroll. Another director could have given the movie a screwball pace and tone, or made it cloyingly sweet, but that would have been a bad choice. They maybe veered a little to far in the 'sedate' direction for this one, but it works.
In 1999 there was another romantic comedy with a crab, Simply Irresistible (with Sarah Michelle Gellar, and Patricia Clarkson). If you enjoyed that movie, I would say this one has a very similar overall flavor...though they are very different movies, and the acting in that one was overall far far better.