I had one of the original GameBoys, so many memories :)

The four games I played the most early on were Tetris (cause it came with the GameBoy), Super Mario Land 2 (awesome), Metroid II (also awesome, at least it was to me) and Zelda: Link's Awakening (even more awesome)

Then, just when it seemed the GameBoy was nearing the end, Nintendo unleashed their evil world-domination virus: Pokemon.  I can't remember how many hours I spent playing Pokemon Red (it was a lot....)

Then came the GameBoy Color, along with Pokemon Gold & Silver.  I think I had about 500+ hours on Gold at one point....

Next came the GBA, and eventually the GBA SP.  The SP is still one of my favorite game systems, simply because it was so small and portable when folded up, plus the battery seemed to last forever on one charge (it would have been perfect if it had a built-in headphone jack...)  And of course, a new model of GameBoy meant new Mario, Metroid, Zelda, and Pokemon games, along with some excellent new franchises (Golden Sun, for example)

I eventually got a DS, but early on it didn't have many good games, so I traded it for my PSP-1000 after a few months.  Some time later I picked up my first Monster Hunter game and the rest is history...

Of course, the old memories never die thanks to my PSP and emulators (though I rarely play Pokemon now, thankfully...)