What set Insurgency apart (and above so many others IMO) was the sheer intensity of the gaming experience. One of the things that was so intense (for me anyway) in Insurgency was the sound of the weapons. Firing an rifle in Insurgency sounded as close to the real thing as I've ever heard in a video game--it captured the "feel" of firing just about perfectly. In Sandstorm, the gun sounds are just not the same. This seems to be a general trend in video games recently, but the guns are very quiet and don't have the same quality report we heard in Insurgency (worst offender that I've heard in Sandstorm is the FAL). Put the Insurgency-style, realistic gun reports back in.
Another of the things that made Insurgency so intense was the scariness of getting shot. It often made me jump when I got shot out of nowhere--you didn't hear the report of the gun and you didn't cry out. You just heard a loud impact and a crack and it was just lights out. In Sandstorm, you can literally decapitate someone with a headshot and then hear them cry out. When a player gets killed, have them stop grousing about it (see next paragraph) at the moment of impact, at least for headshots.
Also, some of the death cries seem to express just ordinary frustration ("Awwww, Christ" etc.) and don't convey the shock and horror of being shot. I like that there are different sounds when players get shot and some of them are great, but removing the tamer ones would go a long way towards bringing back some of the old Insurgency intensity.