It took me awhile to get used to the way it looked and worked...
But compared to hotmail, yahoo, and .mac it is super fast and just plain works. I love it for those reasons. Well, that and it's 2+ gigs of storage aaaaaand the search function is pretty nifty.
Oh oh, that and free POP access means I could finally use Mail.app!
I <3 me some gmail.
As far as spam goes, I don't usually get more than 10 spam emails to my primary gmail account. But I do occasionally get real email in my spam box. No biggie since there's so little spam that I can find those quickly.