SCEE's (Sony Computer Entertainment Europe) surprise hit MediEvil was tremendously well-received when it was released over a year ago, so it's little surprise that a sequel has been in the works ever since.
Video game sequels are a funny lot, while many succeed on expanding franchises and introducing new elements to already established worlds, characters, etc.
A notable chart topper every year since the PlayStation was launched, it would be safe to assume that Tomb Raider 3 stands a pretty good chance of being.