i have the demo of UT2004 and i really like it. but is the whole game worth getting?
If you like the demo, then get the game! There is a reason for demos...
I have the demo too and I played the full at a friends house. If you like the demo you will LOVE the full version! Its the same with a single player and more weapons and more maps :D ITS AWESOME!
I agree with Oompa, if you like the demo, you'll love the full version (you can exchange the word 'like' with a word of your choice, but if you do so you must also exchange the word 'love' with a word of twice the meaning to the word you inserted instead of 'like', for more specific rules see the Dungeon Master's Guide, page 187)