If it's an older Walther made PPK/S, then you have a fantastic little pistol. A bit on the hefty side compared to the ultra-light, super-compact pocket 380acp's out there these days, but they're incredibly well behaved and usually quite accurate.

If it's a newer S&W made one (doubtful, since you said it was your gpa's), then it's still a great little pistol, just without quite as much finesse in the fit and finish.

Either way, my advice would be to buy some ammo and go have some fun at the range with Grandpa's old piece. The PPK/S's are really a joy to shoot. I no longer have a Walther made version, wish I'd have never sold it, but I have a Bersa Thunder (clone copy) and a S&W made PPK/s. They're a bit large for concealed carry in the summer, but I carry them occasionally, and I've even carried the S&W version a bit around town ever since we passed universal preemption in KS.

I suppose a "tell me about the Walther PPK/S" thread wouldn't be complete without acknowledging that it happened to be the weapon of choice for James Bond.