I have mixed feelings about it. I did waste a lot of time in 'the preaching work' that could have been better spent studying (or even playing video games, for that matter). The meetings were a bore and the the assemblies filled me with dread. But I did make friends that I never would have had I not been a JW and despite our current alienation I still love them and don't regret knowing them.
I also enjoyed going out in field service and learning about other people's religious beliefs. While many of them were just Christian fundies as insufferably dogmatic and judgmental as JWs, I also had the pleasure of conversing with atheists, new agers, neo-pagans and ufo enthusiasts. I had a hard time concealing my fascination with other belief systems and often had to remind myself that I was there to tell them about my religion, not learn about theirs.
In retrospect, being a JW meant feeling bored and stifled most of time, but there were just enough good things about it to make me hesitate over regretting I wasn't just raised a Methodist instead. The only aspect of my childhood I totally and unequivocally regret is having to attend public school 6 hours a day, 5 days a week. It took up far more of my time than the JWs did and gave me absolutely nothing back in terms of compensation. I wasted so many hours in what was essentially daycare that I could have invested in really learning something; not to mention all the bullying and sexual harassment I had to endure...