It wasn't the one I grew up with(that was TNG) but it's the purest sci-fi adventure of the series'. It didn't have TNG's soap opera episodes which were frequently sci-fi only in the most surface or casual terms, and it was much faster-paced. DS9 is pretty comparable to TOS in terms of quality, but because of its serialized nature doesn't have the re-watchability factor that TOS has. Also, DS9 went a little crazy with the Prophets/religious stuff in later seasons.
I think if you overlook a few things, TOS holds up very well today, which is a good endorsement of an almost fifty-year-old sci-fi show.