The system reminders app has gotten super buggy in recent years, to the point where I found it basically unusable. I've been looking for a good replacement for it, and after trying many different apps, settled on Due.
Some of the key features for me are Siri support so I can make a reminder when I'm driving, good natural language processing so I can create a reminder without having to manually put in a time/date, and clients for both Mac and iOS. The UI for snoozing a reminder is also excellent, with presets you can set for certain times of day, and buttons to quickly offset from those times.
It's still being developed, which is great. I have two top requests: 1. Have the natural language processing be able to handle creating repeating reminders. 2. Have the natural language processing be able to handle creating a reminder shortly before an event. For example "remind me that I have a doctor appointment at 10am, at 7am on Friday".