I like both products, but if you have the horsepower... get Half-Life 2. Seriously. If you don't have a comp that can run HL2, and don't feel like upgrading, you should probably go with UT2k4. It's not really a "new" game, from what I understand. It's more like an expansion for UT2k3, so I can't see the systems reqs being that much higher.
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