It's hard to know how effective Hal's constructs will be against Ares. The latter seemed to spend more time dishing out destruction than taking it in his battle with WW. And I know Hal had shields but, IIRC, they weren't all that impressive. Granted, it has been ages since I watched that awful Green Lantern movie, so there are probably feats I am forgetting.
One thing that the Green Lantern movie never did was to showcase Hal's power with the ring. We see Kilowog making a freaking miniaturized sun, with no effort. Yet the biggest thing we see Hal pull of is making a trampolin to propel a Gas Tanker into Parallax shooting it in mid air. Oh and the great fist... I think Ares is going to steamroll him, his various attacks, physical strength and durability coupled with his willingness to engage at close ranges will be to much for Hal who never showed himself to be a great Close Combat fighter. Had this been a ranged engagement I could see Hal standing a much greater chance.