It's a squeeze to get my head in, but once its on, its comfy. They are always a tad too snug at first, if they are fitted correctly.
As mentioned, different brands fit differently.
I have a background in medicine from my previous career, and now part of what I do is custom fitting of helmets for our helicopter flight crew members... I'll spend an hour or more on some guys getting their helmets fitting just right, it's important.
There have been lots of times I've been in a shop, looking at helmets, and I'll see some dad fitting his kid for a helmet, basically throws the helmet on, kid says it fits and away they go, with the helmet flopping all around the kids head. I've helped people get a properly fitted helmet, and I don't even work at the place, I just know it's important.
My Shoei cups my head from the top of my forehead, all the way around to the base of the occipital bone and it does not move an inch when I shake my head or nod up and down, without the strap done up. Thats a properly fitted helmet.