Oracle of Ages sports some of the best puzzles in the series, as well as some unique interactivity with its counterpart.
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Zelda: Oracle of Ages is the latest Zelda adventure for the Game Boy Color, and is one of the two Oracle games released simultaneously. Don't confuse the Oracle games as being something like the Pokemon games; both Oracle games are totally different from each other, complete with their own seperate quests. Buying both games would not hurt one bit; in fact, I recommend that you buy both games. The entire quest can't be completed without both games (I'd tell you what I mean, but I'd be spoiling the game).
Ages begins with Link, travelling to the land of Labrynna to seek out Nayru, the Oracle of Ages. As Link finds Nayru, Veran, an evil sorceress, captures Nayru and travels back in time to wreak havoc. It's up to Link to travel back to the past, rescue Nayru, and defeat Veran before she does enough damage to the past (thus affecting the present).
The best thing about Ages are the puzzles you encounter in the 8 dungeons. They're quite challenging, so expect to be stumped on several of them. The boss fights are often tough, because they require more brain power than you usually need in a typical Zelda boss fight. Some of the items you acquire are classic Zelda items, while others are exclusive only to Ages. Items that appear in Ages may also appear in Seasons, but you may/may not be able to upgrade that item in Seasons.
Throughout the land of Labrynna, you will find magic rings, which must be appraised before you can use their effects. There are many rings to collect (60+), and several ways to acquire them i.e. from chests, from Gasha Nuts, etc. Speaking of Gasha Nuts, you get those by planting Gasha Seeds, which turn into Gasha Trees. From these trees, you will receive Gasha Nuts, which contain various items, including rings.
What makes the Oracle games innovative is the interactivity between them. If you finish one of the games, say, Ages, you will receive a password for use in Seasons. Start a new game in Seasons, enter this password, and you will be able to "continue" your quest, and receive special passwords ("secrets") from certain characters in Seasons to use in Ages. Load your finished Ages game, find the person you're supposed to give the password to, and you'll receive a new password, in addition to a nifty item! Go back to your Seasons game with your new password, visit Farore, give her your new password, and the item you received in Ages will now be yours to use in Seasons!
One last thing to add is that if you play the Oracle games on a Game Boy Advance, you get a better colour palette, and you get access to a secret shop which appears only if you play the game on your GBA!
If there are any flaws in the Ages, they are minor ones. First, most of the graphics were recycled from Link's Awakening (Capcom developed the Oracle games, if that's any indication). Second, the interface found in Link's Awakening is used in Ages (and Seasons). You'll be putting that Start button to work!
If I had to decide which of the two Oracle games was better, I'd have to give the award to Ages, because of its greater emphasis on puzzles (which the Zelda games are known for). Both games are excellent, and you really can't go wrong on either one! I recommend that you buy both games, but if you can only afford one, make it Ages.