As a case for the 3DS its neither too tight nor too loose, theres no risk of damaging your 3DS, the material is tough and rugged. There are 3 compartments, 2 of which are zipper sealed, one for storing your games (12 slots) the other as the main compartment for the 3DS (with velcro fastener). The last compartment is only sealed via a velcro flap and has only room for something slim like a dust cloth or possibly the AR cards.
That was the good bit, the bad bit is that on one of the product pictures it shows you a car charger pack fitting in there also, this is misleading as theres no way that the 3DS will fit within that pouch with the car charger pack (or in my case the 3DS's power pack) and still be able to close. The powerpack will just clack against the pocket where the 3DS is stored and wedge it open. Also the main compartment zipper seemed to get stuck on opening 3/4 of the way, it gets caught on the 3DS pouch (may not happen to you).
Overall its a good way to protect your 3DS for streetpass purposes as it is fully protected/sealed, but if you are planning on a longer stay on a journey, you will need to carry your powerpack outside of this case.