I don't actually use the train that much. But they are 100% efficient and effective, yet sadly only 99.9% on time, nowadays.
Security is good; you shouldn't really need to bother much about it. Just take it with you on the train, and leave it by the door, there's space there for luggage. I'm about 40 mins from Zurich towards Germany, so the opposite of from Geneva.
Prices are probably about the same as here in England, although it depends what you're buying. Milk and meat is more expensive, I think, but in general it's about the same. Depending on where you are, it might even be worth popping across the border. Germany is usually a bit cheaper, for example.
I'm sure you'll really enjoy it!!