Personally speaking, with any new venture in life, I always try to ask myself the question if I identify with the underlying cause of the work which I would get to do. The "what" part of the equation is always secondary. If I am not excited with the reason behind the "why" part of the work, then I am sure — however fancy you might have the description spun out — I could never be as excited with the "what" part of it.
At Hashnode, the "why" boils down to this simple cause: "Empowering everyone in the community to help each other to become better." ... And that excites the hell out of me.
A strong cause which you can identify with, (and an awesome team) will always keep you glued, during the bad days; and makes the ride all that more exhilarating, during the good. Now, you generally get all that in a startup, and hence my answer; that's not to say you can't find your cause in a "large" company.
Your work is going to fill a large part of your life, and the only way to be truly satisfied is to do what you believe is great work. And the only way to do great work is to love what you do.
— Steve Jobs