I felt a little like you did, that I was putting all this money away that I couldn't touch until I was 59, in my 401k. But then, I realized (like the other replies here) that the money is (1) growing tax free and (2) reducing my overall tax bucket today -- so while I am annoyed that I will *hopefully* be retired for nearly 20 years before I can touch it, it is smart for me to build it up over time.
I did realize that, with true early retirement (40 or earlier in my book) that I needed MUCH more outside of my 401k - I found that through moving savings around and investing only in regular investments outside of my 401k - we were going to do a Roth, but since we aren't eligible to do a Roth with the tax benefits, after maxing out our 401ks, everything goes to regular investment funds to grow the 'stache that we can get at whenever / however we like.
Right now, our 401ks are bigger than our regular investment stache, which is annoying! But, at least we'll get a nice gift at age 60!