The achievements can give you 250 extra points and most are relatively easy to obtain if you can complete the main quest – for example, you’ll get 20 points just for accepting the mission! There is nothing wrong with some easy points, especially when the original game was rather tough in the achievements category.
You get your money’s worth out of Shivering Isles, even at $30; however the game does use 10% of your available hard drive space on the original 360. You can spend a nice amount of time (more than a weekend, in between eating) enjoying the area and you’ll always be occupied doing something. If you can get over the price, the expansion is an easy sell really due to the unique setting that is completely unlike old Tamriel– the quests make for a more well-rounded main character, making it great for people just starting out as well as seasoned players.