It's horrible and most of the time they will work you to death because it's a "start up" environment. They will try to get you to invest as much time of your life as possible.
Do not trade your life for money.
I thought you could learn new skills in start up because they usually are lean in money so you end up wearing multiple hats. That's good until you realize that most of the people that is in charge of technology are full of it. They buy in MongoDB hype or NodeJS hype without fully understanding the trade off.
You're better off learning new skills on your own time.
If you don't like big company cause of their crazy interview such as Google you can always try medium size companies.