Oh man, I completed Link's Awakening like 5 or 6 times, at least! Sure the graphics are from an 8-bit handheld, but they're actually really good, considering. In fact, imho the 2d GB Zeldas have the best graphics on that system. Besides, after playing the game for a little while you just totally get used to the visuals and just get sucked into the game. It's truly great. And I agree with the comments about PH being a bit... 'empty'. When you play LA or the Oracle games, you'll know. The whole world just seems more 'filled up', and richer in those older games. PH, while still being an incredible game, just doesn't measure up. It feels bland in comparison. Still, it's a grand game too, and I really like the fact that it's all controlled with the stylus too. :)
It's kinda hard to really put into words what it is that makes the gameboy Zeldas, and especially LA for that matter, so special. Also, those games are far harder than PH. Nothing terrible, everyone could complete them if they put the effort into it. But if you compare them to Phantom Hourglass, you'll find the latter much milder and easier.
Ah, and the music. Yes, the quality is of course not so hot, I mean, coming from a GameBoy, but man, the tunes and melodies are AWESOME! Tal Tal Mountains, The Ballad Of The Windfish, The LA Overworld theme... just classic.
Seriously, if you're looking for rich, challenging, hugely fun and AAA quality games, look no further than Link's Awakening and the Oracle games. The first in particular. Oh, and while you're at it, try The Minish Cap. That's another wickedly marvelous game.