I love Sandra Bullock. Primarily because she's cute, but I also think that she's under-rated as an actress. As frivolous as some of her movies may be, she brings depth to her roles that make her characters instantly interesting and empathizable. She was my only interest in The Lake House.
It's a forgettable romance movie with a gimmicky plot, but she's very good in it. I had a hard time buying her as a doctor, but I think that was the script's problem; not hers. We didn't get to see her being a doctor enough. In fact, we didn't get to learn much about her character at all. We don't know why she's so lost and alone, but thanks to Bullock's performance, there's no question that she is lost and alone.
Keanu Reeves, on the other hand, isn't a favorite actor of mine. I like him okay enough in certain roles (Bill and Ted, Parenthood, Speed, The Matrix), but whenever his character doesn't exactly match up with one of the stereotypes that he does well, I usually end up cringing. He's not too shabby in this, but that might be because the script spends a lot more time developing his character than it does Bullock's. We get to see him interact with his father and brother and even if we never do understand why he prefers writing to the unseen Bullock over actually dating the cute girl he works with (who's obviously interested in him), we feel like we know the guy and we feel badly that he's so unhappy.
Shohreh Aghdashloo is tragically underused as a colleague of Bullock's character. In fact, that and my earlier complaint about not getting to see more of Bullock as a doctor make me wonder if there wasn't originally some more hospital stuff in the movie that got cut out for length. 'Cause the movie certainly should've done more with that part of its story.
Still, the movie succeeds in spite of its flaws because it takes two broken characters whom we actually care about and uses them to help fix each other. There's also a nice point to the time-difference gimmick: that when you're in love, waiting for things to happen at the correct pace in nearly impossible to do, but worth struggling with anyway.