Having only read Bonjour Tristesse before this, I'd be very interested to read some of Sagan's later novels and see how her writing evolved. I especially would like to read something a bit longer and perhaps deeper. A Certain Smile is actually a very similar tale to her previous in many ways so if you enjoy one you will almost definitely like the other. As with Bonjour Tristesse, I found this incredibly relatable and really enjoyable to read. Our protagonist and narrator Dominique talks a lot with Luc about connecting easily with another person with such a similar mind, and my experience reading this echoes that, even across the decades, gender and age differences.
Another thing to note is how good the modern translation is, I haven't compared it to any previous ones but the introduction in my edition gave some examples as to why the update was felt to be required. The modern translation certainly has done the job in making it feel very current and, I understand, more faithful to the original French.