There aren't many reasons to buy Lips
The coolest part of the game by far is the wireless microphones that come bundled with the game.
They light up, glow, and change colors. The lack of modes is also disappointing, and without online play, the only multiplayer action you will get is in local play (2 players only).
The simple solution is to buy Rock Band 2 if you are looking for a singing game. Rock Band 2 has twice the amount of songs, better DLC, actual multiplayer, and the ability to play other instruments. Unlike Lips' lack of difficulty, Rock Band provides 4 different difficulties, and a no fail option for beginners.