@ Tigro Spottystripes:
It certainly doesn't hurt to say something like that in a review. It just would be even better if you at least give a bit of an idea what exactly it is you like so much, or of what could have been done better. Perhaps you don't have specific criticism, nothing that stood out like a sore thumb. Maybe it's difficult to exactly pin-point what made the story so enjoyable.
However, even just saying something like "this and this line/scene/conversation made me laugh", or "I cried a little when this/that happened" in an otherwise "plain" review makes it special. Hell, even a line like "I wonder how [character] is going to react to [other character]'s action/revelation/etc." could be enough.
It shows that you read the story and considered it worth another few moments of your time to leave a review, whereas a review like "I liked it. Please update. I wanna read more!" could be meant for any and every story. Nothing in it refers to the fic you just read. It reads like a copy-and-paste response, even when heartfelt by the person leaving it, because it's so generic.