It's simultaneously the most frustrating and the most rewarding experience you'll have. While the reward comes (at least partially) in the form of a great salary (compared to straight web dev), the frustrations are nothing that can't be overcome with stackoverflow and google at your side.
I've been doing SharePoint development since 2003, and the valleys of "I FREAKING HATE SHAREPOINT!" are always off-set by the moments of "DUDE, THAT'S FREAKING AWESOME!"
If you are offered an entry-level position doing SharePoint, I'd take it in a heartbeat. You'll get on-the-job training on one of the hottest technologies around.
