Thoughts on the most difficult instruments for speakers to reproduce?

Lots of good comments in this thread, but the one wild card in all of this is how was the recording made? What kind of microphones and preamps were used? Where were they placed? Was dynamic limiting or compression used? What other processing effects were used in the mixing and mastering process? 

Another problem is that the majority of recordings involve multiple instruments. Different instruments have radically different radiation patterns and interact differently with their acoustic environment, whether in a studio or at a live event. As such, the engineer and producer end up making compromises when choosing how to make the recording. Yes, one often sees each instrument or group of instruments miked separately, but even then they have to be mixed down into a single stereo presentation. That means compromise. Even surround sound (which is often not used with this issue in mind) involves compromises.

Given all of this, I am not surprised that I find most recordings mediocre and some downright bad. It is almost a miracle that a few recordings out there are extraordinary. There really is an art to the process that not every recording engineer and producer possesses.