Hey, awesome question!
I believe the first thing you should concern is:
What exactly is your game?
If you are making a action survival game, go for the action first, make the character move in a good way, a good camera system, maybe some actions as jump and attacking, just enought to feel what the game is, if this part of the game is bad, everything will fall apart, it doesn't matter if your events are awesome and or not.
If your game is not a action title, you can start with the events, maybe a text based adventure with your events can be enought to expose it and find if people think your events are interesting (http://textadventures.co.uk/quest).
The thing is, content should be the last thing unless event IS the game, for instance in Exodemon I made all the controllers (character, enemy, itens, etc) before making the first level.
What I mean is each of these systems should work well alone, but the basic ones will work as a pillar for your game, if this pillar is weak the game will fall apart.
I hope this can help you! :)