The combination of Pac-Man: CE, Rez HD, VF5 Online and Viva Pinata definitely make it worth the money. I'm pretty down on the 360 for having a library comprised pretty much entirely of downgraded PC ports, but those four games are just amazingly rich, unique and replayable.
Rez is one of my favorite games of all-time and I was fairly skeptical because of Q's recent track record (especially when it comes to XBLA) and the fact an outside studio (HexaDrive) was handling most of the port duties. But damn, this really is the perfect Rez. Surround sound, HD graphics sans jaggies, leaderboards, controls that feel exactly like the DC/PS2 editions, awesome visual filters, etc, etc. I'm in love. I'm waiting until the sun goes down to play through it, as I've played through the first level so far and am running score attack to try and get back in the groove. There are some amazing Rez players out there; I'm a very skilled gamer and after two level one score attack tries I'm ranked about 350th.
If I have any reservation about the game it's that I wish it was coming to PSN also, so everyone could experience it. According to the Rez HD xbox.com page, Microsoft Game Studios published this. They don't have a bumper screen at start-up, so I'm assuming MS just threw a shitload of money at Q for exclusivity.