I have no illusions about the startup life, I'm not excited to drink beer with the ceo.

I'm excited by the prospect of owning a technology platform and running with it. The existing tech stack is one outside of my comfort zone (i.e. jumping from windows -> linux), but the architectural & dev principals are very familiar to me.

Solving bigger problems to me means that the company's mission is a good one - working towards a societal good as opposed to building intranets or perosonalizable web portals.