Easy to play with well slotted notes
Same layout as today's popular custom horns
Good value for the money
Can run a bit sharp
Tone has less complexity than some other horns
The Yamaha 667 has grown in popularity over the last 20 years, owning to its consistent quality and Geyer-style design that's becoming more widely used in American orchestras. A custom-made variant, the 667V with a modified Bb slide similar to the intermediate 567 model, is used by many professionals today. Priced about 40% lower than the "V" version, the 667 will suit most everyday players just fine. Its ease of playing and focused sound make it a top choice in both chamber and lighter orchestral settings. The tone quality is on the brighter side, which makes this horn a contrast to the larger, dark Conn 8D and Yamaha 668II sound. Because of the smaller wrap, the 667 only comes in yellow brass which helps to counter the bright tone the smaller bell produces. Note that some players find the yellow brass bell dents too easily. If you are switching from a more sturdy nickel silver horn, be gentle.
Because of its strong reputation in the professional world, a used Yamaha 667 will hold its value well -- better than a comparably priced new Holton or Conn. And thanks to Yamaha's exacting manufacturing methods, you can expect this horn to last a long time with proper care. Some owners claim this horn doesn't project as well especially at loud volumes with an orchestra. The Berlin Phil horn section switched to the Yamaha 667 in the late 1980s for a few years, then switched back to Alexander 103s. They felt the 667 sounds great close up, but not far out in the concert hall. But keep in mind that the "loud" horns tend to be heavier and a bit less flexible. And what's needed in a large professional orchestra may be different than most playing situations. Intonation on the 667 is strong, however players transitioning from larger horns such as a Conn 8D may find it plays sharp. It may simply take a little adjustment to find the horn's center, which is well in tune with itself. Overall, the 667 is one of the best Geyer-style horns you get get for your money.
UPDATE: As of March 2016, the 667 and 667V horns are discontinued by Yamaha. They have been replaced with 671 (intermediate) and 871 (pro) models. These new variations more closely replicate the traditional Geyer design favored by many professionals. One long standing criticism of the 667 has been a lack of projection. The new models aim to solve this with a heavier bell. Unfortunately, the horn sacrifices some of its flexibility and can sound a little dull close up particularly at softer levels of playing. In orchestral settings, however, players may find it cuts through with greater power. Like its predecessors, the new models are in tune and have a focused sound. Check out this YouTube video featuring the new horn.