I've owned my HD 28 Sunburst for about a month now and have barely played any of my other guitars since bringing her home. I'm primarily a jazz player but have always wanted "my" acoustic guitar but (sound cheesy for sure) never fell in love with any I played. They either fought me up and down the neck, or sounded tight, too thin, too boomy, stuffy on and on. You can go to Martin's website and get all the spec's, but I find this guitar a joy to play. The scalloped bracing provides a very responsive top and you can play mellow and soft with great tone...but if you dig in and strum a bit harder sounds just explodes from this guitar. Push it a little too hard and the sound can get a bit mushy, but you really have to crank on it. If you need that high volume I'd go with the standard D 28 with the straight braces.
The Martin HD-28 is an excellent solid rosewood dreadnought guitar. It comes with a Sitka spruce top, Indian rosewood back and sides, and an ebony fingerboard. Unlike the regular Martin D-28, the HD-28 has scalloped bracing, leading to a louder instrument with better projection and (in my experience) better sustain. If you're looking for a really good bluegrass guitar, you have to play one of these. Rosewood dreadnoughts from the likes of Santa Cruz and Collings are also excellent, but they tend to favor the trebles a bit more. They are also more expensive than the Martin HD-28. If you want to read a review of the HD-28 in which I go into much more detail about the instrument, enter Martin HD-28 Horswispr into your favorite search engine and you should find it. The HD-28 is pretty much the "standard" for contemporary rosewood dreadnoughts, and is a "must play" if you're looking for a dreadnought guitar.