I'll throw out the one disenting opinion thus far. I was going to buy one but a friend loaned me his to see if I'd like it. There's a reason the system warns you before every game to only play for 30 minutes at a time that is if you can even stomach it that long.
Regardless of how good the games are you're eyes becomes quite warped by sticking your head in a black box with red lights dancing around. At first you'll think, this isn't so bad, I don't know what everyone else was bitching about. And then you'll slowly start to feel it. It's hard to describe other than you're about to get one heck of a headache combined with a loss of focus. Imagine watching a movie at the theatre during the day and then coming outside to a bright sunny sky. Your pupils are so dilated it's hard to see anything, well, multiple that by 10 and then figure that everytime you need to do anything you're going to get that same feeling. It's annoying as all get out.
I'm so glad I never bought one as it would have just set on the shelf as a collectible to never be played. My Odessey 2 has gotten more love than the VBoy.
If you can borrow one from someone, go that route first, to see what you think. Wario's an awesome game but after 30 minutes, I never wanted to touch the system again.