Hitman contracts is more of an expansion to Hitman 2 than a game on itself, but it's still as good as Hitman 2.
Why do I say this? Well, to begin with, a bunch of the levels in this Hitman entry are remakes of the original Hitman levels, so if you played the original like me you will be a bit disappointed by this.
There's also the fact that this game's missions are just flashbacks, so there's not really any story to the game.
It's still a Hitman game, so you don't need much story, but a little more effort would have been appreciated.
And finally, gameplay wise, it's exactly like Hitman 2, you have your open levels with multiple ways to kill your target, your ability to disguise and your regular weaponry. It really feels like a level pack expansion, something that may have been DLC in these days.
Still, since it's an old game and thus a cheap game, it's worth playing as an expansion to Hitman 2.