Although it doesn't have too much replay value and has a very short story mode, Tomb Raider: Legend is a very good game.
The game, at heart, is more of a puzzle and logic game than an action/adventure title, even though some of the gunfights can be pretty good, even if it's not necessarily the whole crux of the game. The boss battles of the game are just ok, they are very basic and awfully short, and they usually involve their own little puzzle in them.
Like I've said before, the replay value isn't very good, although you can play through the game again on a harder difficulty if your feel like it, but there are also little medallions, called rewards, that you can collect, but you might not find this that entertaining unless you have the Xbox 360 version, because the game offers you rewards for colecting a specific amount of these, but collecting them will also un lock costumes for Lara. Even though these costumes are very basic, they look pretty good, and might be worth it to collect them.
In conclusion, this game is a lot of fun and it should keep you occupied for a little while, especially if you decide to look for all of the games rewards.