With that said, the bad outweigh the good. I don't mean to be a pessimist here (SN is inspirational) but:
1. Their free plan is extremely lacking. You can't even try out many of their editors.
2. Their pro plan mostly only offers editors. I am not sure how having 3 kinds of rich text editors is helpful but they have them.
3. They don't allow any form of account recovery. Which sounds really epic on paper but once you forget your password, you lose all your data.
4. The feature parity between their different apps across platforms is abysmal. The android app is notoriously feature lacking compared to the Web version. (They did put out an update which hopefully changes things).
5. In my extensive usage of the app, conflicts are very normal. I have no issue with that but there's no way to resolve them without creating duplicate copies of the note which clutters up the UI.
5. the UX is poor. No right click on notes, no distraction free mode, no way to collapse the huge notes list.
6. Search and organization seems like an after thought. The only way to organize is via tags. Tags are nice and all but there's not much you can do with them.
7. Their pricing seems absurd.
8. The development seems to be going no where. They are active but many of the above issues are still not addressed.
But as I said, it's not all bad. Most people won't notice the above in their initial usage. They have a solid app with okay features.
If you are a new user looking for encrypted notes and all that hosh posh or just an alternative to SN, you should also give Notesnook[1][2] a try; it solves all of the above issues in a sensible way. Do note that I am the dev so I am obviously biased. It's not perfect but I think it is a better alternative.
[2]https://github.com/streetwriters/notesnook/ (it's not open source but the repo has some good FAQ that you might be interested in reading).