The first season was good, the second season didn't really build on the start that well, but by the time season three rolls into town, it becomes clear that TNG is a series to be reckoned with. Behind the scenes, shake-ups in the writing department had been continual since TNG started, but season three introduces us to Rick Berman: Executive Producer, and even more importantly, Michael Piller: Head of Writing Staff (and one Ronald D. Moore's first Trek script - 'The Bonding' - not a bad episode either!) From this season on, TNG's already good characters begin to grow and become much more interesting, and once sometimes-mediocre stories are replaced with often considered Star Trek classics - season three boasts classic sci-fi 'Yesterday's Enterprise,' heart rendering 'The Offspring,' a TOS crossover, 'Sarek,' and the ultimate cliffhanger, 'The Best of Both Worlds.' These certainly make up for a slow start to the season, and pave the way for a great future for TNG.
Again, getting the season on DVD is totally worth the money - 26 episodes of entertainment, plus over an hour's worth of extra features? Amazing - this season looks at the return of Gates McFadden in particular (replacing Diane Muldaer who played the good Pulaski character, though in retrospect didn't fit into the TNG all that well.) Season three really was a good change for TNG, and could be considered one of its best. Personally, I don't, but at the moment its the best TNG DVD boxset out of the three available.