Both are episodic anime covering a small number of girls with no real connections. Both of them are based of Visual Novels that also share a multitude of similarities. Both series are 12 episodes and easy to watch over long periods of time since episodes have little to nothing to do with each other. Sentimental Journey's focus changes every episode, while Diamond Dust Drops Focal Character changes every 2 episodes.
Both anime are 12 episodes about a group of girls linked together by episodic love stories. Very similar. Hatsukoi Limited has quite a bit of fan service though (which is odd, considering it's marketed to girls, right?).