I had to take two runs at this movie. You really have to be in the mood for a dark, plodding movie that hits hard if you give it time to set up the opportunity.
The film touches upon themes like "be careful what you wish for" and "the easy way out may not be the best". Winslet and Carrey are good in their roles. Clementine (Winslet) is spontaneous, flakey, and Carrey is dark, brooding...but they match. There are some very emotional scenes, but not in the typical romantic comedy sense. As whimsical as the premise of the movie is, there's some very real heartbreak and dark reality built in.
Characters are various shades of grey. You'll see hints of selfishness from the main characters, and supporting roles turn out to be just as flawed if not dispicable. There's subtle and sometimes ludicrous humour to be found as well.
All in all this is an excellent film, but I recognize it's not for everyone. If you're looking for a laugh-out-loud comedy, look elsewhere. If you're looking for a romance story to score brownie points, or to make yourself feel better...also look elsewhere. This is a film for when you're looking for something odd, dark, deep, and takes time to let you appreciate it.