This first Xbox LIVE 'Games with Gold' freebie for July is not Halo 3 or Assassin's Creed II; instead, the free game is one the first tower defense games that really made the genre what it is today; it's a great game, but it is old and not as seemingly substantial as the retail games mentioned at E3. Why no Halo or Assassin's Creed? It's because they never specified a date for either game, only saying they were two of the titles they would be offering over the next few months, so don't get your panties in a bunch. That said, I would still like to see games more current than any of the games revealed so far because, at the rate of one free game every two weeks, we'll never see anything even remotely current.
Defense Grid: The Awakening [XBLA] - (800 MS points ---> FREE)
And remember, the Xbox LIVE 'Games with Gold' promotion is only open to Gold members (thus the name), so if you're rocking a Silver (Free) account, you're shit out of luck.