Pros: Sound quality, Built quality, Battery life
The playback portion of D100 has been optimized comparing to its predecessor D50. It can also playback flac and aac regardless of its inability to record in those format. It also feature multi language interface. Build quality is good, full metal construction. It also run on 4 AA batteries, and has good battery life, with back lit off, it can play for 24 hours straight.
runs on AA batteries
dropping it isn't much of a problem
gapless playback for PCM and DSD
lag free interface, no file search time, no boot time
can drive most portable headphone well
Heavy: 430g (0.95~ pound)
Channel imbalance at low volume, sensitive balance armatures is unlistenable (lowering the gain on music files or adding resistor cable can solve the problem)
attention magnet: better not have this out of the pocket when outside
Overall, the D100 is slightly warm, very detailed. Instruments are better presented than vocal, sound is spacious and transparent, the soundstage is not too impressive however. The low on the D100 is a bit more than neutral, fast, punchy and extends deep. it makes instruments sounds very dynamic. The mid is detailed and full, the vocal will standout quite a bit, and this really shows when using V sounding headphones. The high seem overly extended when playing PCM files, it makes female vocals sounds great, lots of overtone, but can be tiring, and sibilance may be a problem for some people. in terms of highs DSD file sounds more relaxed.
Headphone choices: I really enjoyed paring the D100 with sr325 and er4s, I believe these two phones are great for vocals. the D100 is very forgiving for headphones choices,