Saying that it's fun while it lasts isn't so bad, since the game is so chock full of fun you'll play it over and over again anyway.
For those that aren't aware of it (and there are many that aren't), Nightmare in Dreamland is actually a port of Kirby's Adventure for the NES. Like the Mario Advance games, the graphics and music have been completely redone to fit the GBA's more powerful hardware. What this Kirby game winds up being is a really great Kirby game that looks great, plays well and sounds nice, but is far too short for its own good.
The game's story is pretty standard Kirby fare. When Nightmares start showing up in people's dreams, Kirby finds out that King Dedede has stolen the Star Rod. Since the Star Rod is needed at the Fountain of Dreams, Kirby goes off to recover it and save all of Dream Land, etc. Been there, done that.
The game is set up in worlds and stages. Each world has a series of doors that Kirby must go through, from the six stage doors to the bonus game doors. In the stage doors, you'll need to go through a standard Kirby-like platform level, sucking up enemies and copying powers (about 20 different kinds in all) to make your way through. Bonus game doors are where you can earn some 1UPs for the normal game by trying your luck with the sub-games available to you. (More about those later.)
Usually, these bonus doors are hidden, and need to be uncovered by finding secret rooms and switches within the stage doors, some of which require some really crafty thinking. As any Kirby fan knows, inhaling two powers (in the form of enemies) at the same time will create a roulette effect, giving you a new power. To find all the secrets, you're going to need to figure out which two enemies give you which power, and when to use them to get through some of the obstacles blocking the doors. It's pretty nice when you break through, though.
As for what you're seeing while you're playing, the game looks awesome. Everything is nice and colorful, with lots of animation for Kirby, from the sucking to each and every one of his numerous abilities. The sound is very good too, with some nice touches you'll hear from time to time. Sometimes you’ll hear Kirby shout out in pain, and he'll squeak when falling down from high ledges. Music is classic Kirby and very good (especially with headphones). It's a really cute package when you put it all together.
Unfortunately the controls hamper the gameplay. Jumping and floating are done with A, while inhaling and using abilities are done with B. However, you can also jump and float by pressing Up on the control pad. This might seem harmless at first, but it becomes a nagging annoyance once you're familiar with the controls. You can only use ladders if you start climbing from the bottom, otherwise you'll need to float up, which is slower. You'll also find that you'll accidentally hit Up while jumping, which will cause you to hang in the air longer than you'd like to, which is an annoyance during boss fights.
Another strange control quirk is that the L and R buttons aren’t even used. This is made more mysterious since dumping a power requires you to press Select. It seems that Nintendo and HAL decided to copy over the NES controller exactly to the GBA, which is a little dumb with two extra buttons at their disposal.
The other major downfall of Nightmare is that the main adventure game is short — really short. After playing for about 30 minutes, you'll find that you're already 50% through the game. (Speaking of, if you know where to go and what do to, you could blast through the whole thing that quickly.) Although this is really an NES game you're playing, this is still really a letdown since the game is so much fun to play, by the time you're done with it the first time; you'll wish that there was more to do. Some of the game's extras however, give you an incentive to come back to it.
The three sub-games available to you from the start are Quick Draw, Kirby's Air Grind, and Bomb Rally. The first has you test your reaction time against an opponent, the second has you grinding rails in the air, and the third is sort of a hot potato game with a bomb. All three of these feature single and multi-pak modes for four players. The entire single-player adventure can also be done cooperatively (multi-pak). The first unlockable sub-game is the traditional Kirby Boss Battle Endurance mode, and there's another sub-game to reward you for completing the game all the way, but we won’t give away what it is. It's worth the time you put into the game to get it. All these modes are great to play by yourself and more fun with friends and link cables.
Other than the control and lastability issues, this is still a Kirby game, and because of that, it's automatically fun. The game is short, but sweet enough to buy for all Kirby fans. With all the secrets to find in the main game, a few of the tough ones will get you thinking, but you'll blast through the game sooner rather than later. However, the extra games you'll uncover do provide plenty of replay value.