This boxed set, while a bit more pricey than any individual DVD, is well worth the money. It contains every episode from Pokemon Advanced DVD volumes 1-4 (with approximately 7 episodes on each of 3 discs, for a total of 20). Purely in economic terms, this is a major bargain; buying all 4 volumes individually would run between $50-$60, or about $15-$25 more. If you are going to get the Pokemon Advanced DVD's, by all means, get them this way and save yourself enough to buy another DVD.
As far as the content: die-hard Pokemon fans would buy these episodes no matter what, so my only advice to them is the economic sense outlined above. If you're one of the many people who are probably a bit undecided on these episodes, I would recommend giving them a chance. If you never watched any of the later Johto League Champions or Master Quest episodes, then you will notice that the animation has improved significantly since the first couple seasons. Misty is gone, replaced by a girl named May (who was modeled after the heroine from the Ruby & Sapphire GameBoy Advance games). Make of that what you will; if you are a Misty fan, you will be disappointed, and vice-versa. Personally, I am of the frame of mind that, while she is in some respects a more interesting character than Misty (she starts out disliking Pokemon and gradually comes to appreciate them), she is not, and never could be, a suitable replacement for the character who captured my heart 8 years ago and had been a permanent cast member for 5 full years. In any case, she and Ash are joined by Max, May's younger brother, and, as the box art implies, Brock ultimately returns to the team in about the 4th episode. Both Ash and Brock sport new, different looks from those with which we are oh-so-familiar from past episodes, and Ash has matured somewhat since he left Pallet in the 1st anime episode from 1998. Team Rocket is omnipresent, as always, and the storyline primarily follows that of the Emerald version (villains from both Team Magma and Team Aqua drop in from time-to-time; we ultimately see both of the Ancient Legendary Pokemon that grace the games' boxes; and Juan is the Sootopolis Gym Leader, not Wallace). They tend to follow the games' storyline more closely than the Johto episodes did. To somewhat disenchanted Pokemon veterans: these storylines are generally better than many of those from the Johto continuity. Most importantly in my mind, they don't waste nearly as much time as they did during the middle and end of the Johto episodes.
Basically, I would highly recommend this release to anyone who really likes Pokemon, and also to those who just-plain like it.