I'm sort of surprised that when Mozart recommendations are being thrown, ye good ol' Eine kleine Nachtmusik never comes up. Is it just because of its obnoxiousity or is it considered a lesser work by people in the know?
Because even though it's been spoiled by over-usage, I still find it to be one of the most charming musical pieces ever written, perfectly representative of what Mozart (to me) is about.
It is both charming and representative of one side of Mozart. But it is also comparably lighweight, modest and because of its ubiquitious presence it seems precisely one of the pieces people who find Mozart shallow or boring have in mind.
It does hardly show the passionate, operatic side of Mozart that is present also in some instrumental pieces like the g minor symphony, nor the "intellectual" side of some string quartets, quintets, or the "Jupiter", nor the brilliant instrumentation for winds like in the "Gran partita" or the piano concertos K 482 and 491, nor the grand choral writing of the Requiem and c minor mass. As there are so many great works by Mozart, the Kleine Nachtmusik has to count as a lesser one (it even says so in the name!), despite its not unjustified popularity.