Let's start out with some pictures of the item in question.
(Grr. Sorry for the blurry pics. I still haven't learned how far away I need to be for my camera to focus on something.)
Helmet Front View, helmet side veiw.

The Good:
General
It's the ROTJ reveal helmet, so it comes apart in three pieces, the dome, the mask, and the neck/collar piece. It includes a stand, to which the top of the mask attaches quite securely. Also included were a couple pieces of paper: instructions for assembling and disassembling the helmet; blueprints which explain what some of the detailing is supposed to be.
Dome and mask, dome, mask and neck, blueprints.

Size
It's 8 inches tall, a little under 5 inches wide, and about 6 inches deep. Since it's a 45% scale helmet that means I could display two of these in place of a single full size helmet. That's a good thing.
Helmet compared to a Hasbro Vader figure.

Detail
It seems nicely detailed to me, the mouth and chin vents have the appearance of a screen behind them, the mask has the two tone paint job that I've come to love - although it's black and dark grey, rather than black and gunmetal silver like I like (although that could be a ROTJ thing vs ANH - see Accuracy below). The lenses are see through. Removing the dome you can see the cool detailing that was seen in ROTJ, some molded in the plastic of the mask, but the gold greeblies and the red/silver vent looking things are separate pieces that have been glued in. The collar is also nicely detailed, showing the stud thingies, or whatever those things are that are on the collar. They're not as shiny as I was let to believe they would be from the box art. On the inside of the neck is a representation of the breathing apparatus - tubes, wires, etc. Pretty cool looking, in my opinion.
Mask front, mask side, mask back, mask top.

Quality
Not as much to talk about here. The breathing gear is metal: thin metal tubes, metal nostril plugs, thick braided metal wiring, and real plastic insulated wires. This is the heaviest piece of the helmet. The stand is pretty sturdy, with a metal plate on the bottom to weight it and keep it solid, and three rubber pads on the bottom.
Neck side,
neck from top.

The Bad:
Quality
Material - it's mostly plastic. The dome is plastic, and isn't as shiny as I would like, and it's slightly scuffed up. The upper mask is plastic. The circular detail on the very top may be aluminium, I'm not sure. The dome and mask are very light and feel cheap as a result, especially compared to neck piece.

The Unknown:
Accuracy. Being that it's a reveal helmet I assume it's meant to replicate Vader's ROTJ style helmet. I'm not knowledgeable enough with the intricacies and details of the small changes that distinguish between the movies, other than to say it is definitely not an ANH helmet. If someone from the RPF or The Prop Den is reading this and can chime in here, that'd be great.

Conclusion:
For what I paid for it ($33 shipped), it's a nice display piece. A pretty good compromise between material cost and quality. For the retail price $75-$90 I don't think a lot of people would be pleased with them. The Vader, because it is more complicated than the other helmets - I don't think any of the others come apart - would probably be the best one, and I think I'd have still been happy with it had I paid $50 for it. I'd still like to hunt down the Boba Fett and Stormtrooper, but I'm certainly not going to pay the $130+ the Stormtrooper helmet goes for on eBay, nor will I be very willing to pay $30+ for Boba, since it's not multiple pieces that I know of, any internal details are not ever going to be seen.
More info on the Riddell Star Wars helmets.

Really, though, it's too bad this line was cancelled before all the helmets I would have purchased were released. I'd love the remaining Imperial helmets in this scale, as it's a very nice size: Scout Trooper, TIE Fighter Pilot, AT-AT Driver, Snowtrooper, and Royal Guard. It would be pretty cool, in my opinion, if Master Replicas would produce a .45 Scaled Helmet Line.