Yes, they are absolutely supposed to feel big. They really shouldn't touch your toes or the sides of your feet. But if you really think they're WAY too big, you can stick them in the dryer for a little bit. It shrinks them some, but just don't do it TOO much.
I have awful, terrible, messed up feet. They hurt pretty much if you just look at them wrong. I am an avid fan of the Crocs at Disney. I used to wear my tennis shoes, which I hate wearing b/c they make my feet SO hot and are so heavy. But I knew it was my best bet for cushion. Still, at the end of each day, I always had the "hot" spots on my feet and my hips and feet were in so much pain. I remember trip before last finally having to leave Epcot...well, actually, literally hobbling back to the buses b/c I couldn't take one more step. Last trip was my first trip with Crocs. Did my feet still ache at the end of the day? Sure! But they didn't HURT. Just a little tired. My hips didn't ache like they normally would. I had no blisters and no hot spots. My feet never got sweaty and overall my body stayed cooler b/c the Crocs were way better ventilated than my tennis shoes. We did so much walking in that trip that DH and I both ended up with chafed legs from the seams and cuffs of our pants. But our feet were fine
Personally, Crocs are a fashion void. But I still wear them, and I will even wear them with socks if it is cold and I am wearing jeans. However, there is no way on this green earth you could get me to wear socks and crocs with shorts. That's just asking too much of me
About the Mary Janes. I LOVE mine, but I've always said they have half the shopping life of regular Crocs. That means after half a day my feet hurt. I use them for shorter walking trips.
The other good thing about Crocs is that when they are new, they have amazing traction. With any other shoe, I just think about a puddle of water and I can slip. I approach a damp, slight inclines and I start scooting by inches b/c I ALWAYS slide. But these suckers have amazed me time and time again. It's like they stick me to the earth. However, I have heard that as they get older and the tread wears off, they get slipperier. My Crocs are going on 3 years and still no problem. Though don't try to turn without lifting up your feet good and high. The edges of Crocs are a little TOO good with traction, and I've seen alot of people listing over.