I'm also a Green Mountain Grill owner. A couple of my friends from church had Traeger grills, and really liked them, except for the controller. The Traeger controller is only adjustable in about 25° increments, and sometimes runs a little hot at the all important 225° setting. The Green Mountain Grill controller adjusts in 5° increments, and it will go higher in temperature also.
We've really enjoyed it, and have tried a lot of different things that we had never had before. I've done ribs, Boston butts, brisket, tri-tip, roasts, Thanksgiving turkey, salmon, prime rib, made great beef jerky, and many other things. They have all turned out great. Now, prime rib at a restaurant just doesn't measure up.
One weakness is direct heat cooking on pellet grills. They just aren't that good at it. Some brands have tried a few different gimmicks to do better, but none of them really do well at it. I would recommend keeping a gas grill or charcoal grill for cooking burgers and steaks.
If you do get one, keep in mind that not all wood pellet brands are equal. Buying quality pellets makes a lot of difference. Traeger pellets are OK, but nothing special. The best I've found so far is Lumber jack. They are well worth the effort of finding a local source.
http://bbqlumberjack.com/our-pellets/