Xonotic.

Great arena shooter all around even excluding the fact that's FOSS. Used to play it with a 2012 Intel i5 and HD 2500 integrated graphics on 1080p medium settings and was averaging around 80-90 FPS on default maps.

Now I don't know what kind of GPU do you have, but I bet that it would probably just fine on low settings and maybe at a lower resolution.

Another thing worth mentioning is that you may have trouble finding populated games with good ping if you live outside of Europe.