I've had this helmet for a few weeks and feel very confident in the level of protection it offers. I measured between the medium and large, and based on some other reviews, went with the large and it is a good fit.
I live in Miami and it's summertime...it's hot! It's hot without a helmet, so of course, it's going to be hot with one, regardless of color. But I feel as though the design of this helmet lessens the discomfort by providing a gap between the top of the head and the helmet, so it is surprisingly "cool" inside the helmet. There are a number of vents that allow the heat to escape, and any heat that builds up is pretty much sucked out when you start moving. The airflow is pretty good with all of the vents open, and cracking the shield open at low speeds provides additional flow. The numerous detents offer a good selection of positions.
The fact that this helmet comes with a clear and dark shield make it a very good value. I also think the dark shield adds to the cooling effect. Beware that when you go to change shields you are going to feel like things are going to break due to the plastic parts. It took a little getting used to, but once you get the idea of how everything works it isn't too hard. Not the easiest or quickest system out there though.
I wear glasses and due to the close fit of the padding they are a tight fit. They are thin wire glasses too, not thick bulky ones. Having said that, they do fit inside the helmet and do not hit the shield. Just be prepared to have to adjust them from time to time.
As some others have noted, the helmet is noisy at higher speeds. By this I don't mean road noise, I mean the the sound of the air rushing past the helmet. I ride a KLR 650, and the windshield pushes the air upward in such way that it seems to be directed at my head, so this could exacerbate the problem in my case. The helmet seals well in the front, and I have not experienced any fogging. I expect the some of the noise may be a result of the air passing by the vents, so perhaps this is the trade off for the ventilation.