I have the 8' 4wt. and am singing its praises. I have been fly tossing for over 30 years, so I've cast a lot of rods and can shoot a full line when called for, so I feel justified in saying that this will hold its own with anything in the $300-$400 range. Light, powerful, and with a reasonably sensitive tip by today's super fast standards. It actually casts much better with a 5.5wt. line and strong double haul than with a 4wt. line, and shoots ridiculously tight loops. It makes a solid 5wt. rod, actually.
The components and build quality are very good and appealing, regardless of price. Even an experienced caster should have a hard time justifying spending another $550 for a top-end rod which gives very little improvement in performance over this model.
I don't have much experience with fly-fishing, but after suffering at the hand of my friends' beratement for long enough I had them recommend a rod for me as a beginner. This is the rod they recommended and I haven't used it much but as someone who's just learning to fly fish I've had good luck with it.
The reason they recommended it to me is that the places where I join them in fishing, there tends to not be a lot of room for a longer rod. Plus it tends to get windy and the action on this rod is easier to cast in windy conditions.
I've had some good luck with it so far and hopefully will have more in the future.
After reading the 5 Weight Shootout by Yellowstone Angler, I bought the Greys GRXi+ in a 9' 5 weight with the intention of using it as a 6 wt. rod. It is an amazingly powerful rod, and throws the WF6W line with ease and accuracy. One thing to be a little careful of, the stiffness of the tip means you need to have a light touch when setting the hook with light (6X) leader. I forgot and broke a fish off yesterday at the set. Other than that, it is a well built, sturdy, good looking rod and a super deal for the price. Don't be afraid to overline it.
I fish the rod in the 9' 5 wt model a lot. Use it a lot for clients on guide trips because it is versatile, easy to cast, and the price is right. This rod has plenty of power for nymphing and streamers, but will still throw a dry nicely too.
I just recently started using this rod, and it has a great action, and would certainly go up against any rod priced $100 higher than this. Got this along with the Greys reel, and I love the set up!