Just my two cents, subjectively of course: shooters are fun, I love them too, but this theme (rescuing dogs) calls for less violent gameplay in my opinion. Maybe a narrative game, like a Twine or visual novel, would be more appropriate. Also easier to make, if you're just starting out with game development. Failing that, maybe a game where you race around town, say in a car, and collect tokens / dodge obstacles / trick bad guys to reach dogs in need on time. What genres do you like?