Terminator Salvation adds nothing new to the third person shooter formula, and it has no replay value to make up for it.
Terminator plays like any cover-based third person shooter, except with zero bells and whistles. The lack of variety in the gameplay does not help. There are very limited amounts of weapons. I counted 5 weapons throughout the game. A machine gun, an assault rifle, a grenade launcher, an RPG, and a shotgun. Enemy types don't spice much up either. You have Spiderbots, T-600's, Aerostats (wasps), and T-700's. None of them really offer a challenge, even on hard difficulty, most of them can be taken out with a couple grenades and a couple shots of the rocket launcher. If you're looking for variety in your gaming Terminator Salvation is not your best choice.
Beyond being unoriginal and repetitive, Terminator: Salvation has the gigantic problem of being way too short with no replay value. The game can be beaten in 6 hours on the hardest difficulty. There is no multiplayer, no extras to collect, not even a quick mini-game. After you beat the game, you have the choice to play it again, or stop playing it completely. I chose the latter. Hard isn't much of a challenge either, if you've beaten Gears of War on Hardcore difficulty, this should be a piece of cake. As long as you stay in cover and flank your enemies, Terminator's hardest difficulty is a cakewalk.
That brings me to my conclusion, with an extremely short length and no multiplayer to speak of, Terminator is not at all worth $60. In fact, I wouldn't even pick it up at $20. Terminator is an alright rental if you're looking for another generic shooter or an easy 1000 gamerscore, but there is absolutely no reason to buy this at full retail price.