The classic arcade games ported to the Gameboy in a two pack, and a rather good port it is.
The gameplay of both is rather simple. In Joust, you run around on your ostrich, using the flap button to make your ostrich flap its wings, pressing repeatedly allows you to fly. You then move around the static screen, multi-tiered stage and try to land on top of the other nights on their ostriches to destroy them, and then collect the eggs that appear so that they don't come back. Then in later levels you have lava to contend with and the occasional pterodactyl, that can only be slayed by very precise timing and handling. A remake of the classic is also included, that while having rather identical gameplay, has updated graphics and a screen that moves to make it a little more challenging as you can see all your opponents all the time any more.
In Defender, you fly around on your spaceship with the ability to fire your laser cannon at all the varied alien ships coming to abduct the people on the surface. Lose all the people and the planet surface explodes and you have to contend with all the alien ships coming after you, along with some rather hard to handle ships. You also have a hyperspace function to try and get out of trouble if there are too many ships for you, but it may make things worse depending on where you end up.
As stated, the gameplay is rather simplistic, so if you are looking for some very deep game with a wide range of various controls and weapons at your disposal, your best bet is to look elsewhere, however if you enjoy the simplistic, classic gaming styles of the old, classic games, you most likely know what to expect gameplay wise from these two.
Graphics and sound were very good for the time, and they make a good showing on the Gameboy as well. By today's standards they are severely lacking, but the detail of such old games is still rather impressive and if you can get past that these graphics and sound are from the 80's, and thus very outdated, you will still find a very appealing game. If you cannot do that, you may try picking up the GBC version, or just passing on the game all together.
The value on these games is what makes them extraordinary and truly classic. Like a game of cards, no matter how many times you play it there will still be challenges (for most people), and they will still be fen every time you come back to them. You won't get so bored with the game that you won't want to play it again and will find yourself coming back to pick it up again and again. The port of the game is admirable and keeps the same, great level of control, gameplay, and graphics (though on a smaller screen and without color) as the originals did and it is worth it to pick up this game for a fun time. Just don't expect anything grand or revolutionary about them.