The demo runs great on my system, in the sig... but the demo compared to the retail version may run a bit differently.... following in a portion of the readme from the demo...
0.2 Features of the demo compared to the full version
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The full game differs in the following ways compared to this demo:
* Textures in the full game are, on average, 2X higher resolution
than in the demo. The textures in the demo were reduced because
of download size limitations.
* The full game includes over 100 maps, compared to the 5 in the demo.
* The full game includes over 80 characters, versus 4 in the demo.
* The demo only supports "instant action" mode, Internet and LAN play.
The full version also contains the new single-player ladder, enabling you
to play through the game while managing a team roster.
* The demo doesn't include the Unreal editor and content-creation tools
which ship with the final game, enabling you to build new levels, modify
existing ones, and create game mods.
* The demo doesn't include any mutators, but the full version includes
over 20 mutators offering new variations on gameplay.