Not exactly challenging, but very enjoyable and memorable.
Wario can get a few different abilities; coins; or hearts, 100 of which gain him a free life; from blocks hit in the same way as in a Mario game (jumping) or by pressing the B button and charging. It's a very simple game, but a little more complex than your average Mario game of the day. The abilities are pretty cool, but there aren't very many. One allows him to breath fire while another gives him jet-like boosters on his cap to make him fly straight forward for a long distance. This adds a bit of variety to the traditional platforming style, which is always nice. There isn't much of a story, but you find out at the end of the game that all that you've just done was for Wario to get a wish from a genie for a mansion. The graphics are... well... GameBoy graphics, but they really aren't too bad, considering. I had a very hard time beating it when I was younger, but playing it now was a piece of cake.
Wario Land is a great game. It's probably my favorite 2-D platformer I've ever played and it's a definite must-buy if it can be found on Amazon.com or eBay for a decent price.