Re: SUPER UBER SPOILERMANIA: The Ending... What Does It Mean?
Loki has fooled Heimdall, who was said to be more powerful than Odin. He's also a cold, calm and calculating individual who's been observing the Universe for a very long time.
Thor is a hot-headed, relatively inexperienced guy with little knowledge about magic (he's been fooled by Loki's ilusions way too many times) and who had just lived through a period of emotional turmoil. He's also less intelligent than Loki.
So yeah, Loki fooling Thor is just business as usual.