I'm a few weeks into working at me.dium, and the differences between a big multi-billion dollar company and small start-up are really sinking in. The excitement level here is invigorating. Knowing everyone in the company provides a level of mission, and capability, understanding that large companies lose. Big companies can obviously scale, but distance naturally grows between the board's goals, and what the troopers on the ground are doing day in and out. That's probably fine most of the time because a big company has big dollars (cash or debt) to spend on the inefficiencies, and gets itself from point A to B. A small firm literally can't afford these inefficiencies for very long (though it has others).
I'm loving the tight coupling between dollars and activity at a startup. Every dollar matters and people are aware of the value received in exchange for that dollar. Large companies (at least those I've been involved with) abstract the connection between that value and the actual dollar spent into oblivion; you lose track of the revenue-expense feedback loop which is vital.
I'm really enjoying the constant push/pull of the fight-to-live atmosphere here. Minute to minute, things change. Your assumptions in the morning can be drastically different in the afternoon. While challenging, it's great mental exercise; a true growth opportunity for all those involved.
Personality dynamics are present at all times; this is both good and bad. In a large firm, you can carve out a portion of the organization to include/exclude folks. You can build your own "click" (not that I ever did this (I hope), but peers of mine certainly did) or navigate to a "safe place" in the firm. In a small firm, everyone's in the room, all the time. You're forced to deal with any conflict and friction, right there, on the spot; much more healthy in the end.
Onward and upward!