Kirby's Adventure takes Kirby through 40-or so levels spread across seven different worlds. Each level consists of multiple sections which are populated with platforms and numerous enemies. Boss battles appear throughout with a tougher one at the end of each world.
The platforming doesn't require as much skill as a game like Mario, so it will appear more to those wanting less of a challenge. There's some difficult sections, mainly due to the amount or type of enemies.
Kirby can walk, jump, and fly to navigate through the levels. Flying can often bypass large sections rather cheaply, but there are plenty of flying enemies to cause you trouble.
Kirby can suck enemies in to defeat them. Then you have the choice to either launch them as a projectile, or swallow them to gain an ability (or nothing, depending on the enemy). These abilities include breathing fire, equipping a sword, turning into a rock, transforming into a wheel Etc. If Kirby is flying, he can exhale a puff of air which not only causes him to fall, but acts as another form of attack.
There's several bosses that you battle throughout the game but they usually require the same technique to take them down. Dodge a few attacks, wait for stars/projectiles/enemies to appear. Inhale them and fire them back.
On the bottom of the screen, there is a HUD that shows your health bar (Kirby can take 6 hits), bosses health bar (if applicable), points total, current ability and amount of lives.
The graphics are simple, but it's really impressive given the technology at the time. It's always clear where you need to go, which objects pose a danger, and which objects you need to interact with.
The levels are selected in a hub-world. Completing one unlocks the next, and previous levels can be replayed. There's some optional mini-games too which give you a chance to earn more points and extra lives.
Once, you complete the game, you can try to obtain the best ending by replaying the levels until you've found every hidden switch and bonus room in the game.
Overall, Kirby Adventure is a decent game with plenty of ideas. However, the platforming aspect is undermined by Kirby's ability to fly, which means the enjoyment is provided by the action elements. For me, this wasn't that entertaining.