At a minimum, you should save enough to your 401K to get the company matching.
  Let's say the company match 50% on the first 6% you save.
  So if you put 6% of your salary to 401k, the company will add another 3% in addition to what you did. That's a free 3% raise. 
  Tell me another way that you can get guaranteed 50% return of your money.

 
  In addition, there is the tax advantage where you do not get taxed on your money until you retire. So you money grow without taxes until you actually need them.

  Are there bad 401k? yes, but I think very few. Check the rules of your company. But most of them are very good deals and you should take advantage of them if you can.