I played football from age 9 through 22, with a modestly successful career as an offensive lineman playing at a small college, and have an assortment of friends that played on all levels, including a longtime family friend who played seven years in the NFL. Believe it or not...I have a few thoughts. Much of this will echo some of Evolv and FlatsFarmer's comments.
Let's start with this: the game cannot be sterilized completely from risk. That doesn't mean we should throw up our hands and not even try to improve things, but we must acknowledge this fundamental reality: the fact that it's a "contact sport" is a large part of the appeal, and no one would watch if it was just transformed into a game of flag football. There will be broken legs, broken arms, torn-up ligaments, and yes, concussions.
On the flip side: there are absolutely things that can be changed to make it safe-er than it is now, and most guys who complain about flags on helmet-to-helmet hits by saying things like "this is ruining the league" have probably never been had their head smashed in by a 230-pound man running full speed (and their full speed is a whole lot faster than yours) with a 20-yard running start.
Here are the changes that I would make:
1) Defensive backs are no longer allowed to break up pass attempts by targeting the man catching the ball and obliterating him right as the ball arrives; the defender must make an attempt to actually make a play on the ball (very similar to the way basketball defense must be played - you can steal a pass by intercepting it before it reaches the man, but you can't just run up and clobber the guy as he receives a pass).
There are plenty of violent collisions in the interior line, but the truth is the most cringe-worthy hits for me to watch as a fan are the hits where a safety lines up with a 20 yard running start and earholes a wide receiver trying to make a catch along the sideline. In that situation, IMO, the safety should have to actually attempt to break up the pass by deflecting the ball. If he blatantly ignores the ball and just crashes into the receiver in a naked attempt to separate ball from man...I'd make that a penalty.
2) In a similar vein: every tackle attempt would have to include a genuine attempt to "wrap" the man and bring them to the ground. No more "tackles" that involve "run at the guy and just dive into him as hard as possible with my head down." The defensive player should not be allowed to merely topple the offensive player like a bowling ball taking down a bowling pin. For example, a tackle like this...
...in which the defensive player makes NO attempt whatsoever to wrap his arms around the offensive player would be flagged. Tackle attempts that must involve a bona fide "wrap" attempt are, by nature, going to be a little less violent because there's no option to just use your body as a missile and dive at someone.
No doubt this will bring complaints from defensive players that it makes their job harder. Yes, I know. Too bad! Every team's defense will have to play by the same rules. If it makes the games higher-scoring, so be it (or better yet, the NFL could adjust a number of other things that would make it a little harder for the offense as well - for example, starting on 1st-and-15 instead of 1st-and-10).
I would absolutely NOT remove the helmets.(or its cousin "remove the facemask"). I've never really bought this argument that taking the helmet off will make the game safer because it would inherently force guys to stop leading with their head...I think that's true, but I'm also guessing it would also lead to a lot more fractures of noses and orbital bones. You can make a decent argument that just turning the NFL into rugby would be a cool thing, but that's a different reality I'm not going to discuss here.
It's a physical game, and there always will be injuries. The thing that's bothered me most about retired NFL players in crippling condition is not their physical condition itself - realistically, that's something everyone who played the game had to know was coming - but rather the cold, callous manner with which the NFL handles the crippled retirees. The league could have done itself a world of public-relations good by announcing (as soon as there was PR smoke around this issue) that all retired NFL players who spent at least X games on an active roster would be offered comprehensive medical-insurance coverage for life, and from this day forth all currently active players who appear in at least X games will receive the same benefits package on the day of their retirement.
Much as Evolv has noted - I also believe that the benefits of playing youth sports far outweigh the drawbacks, even with something as "dangerous" as football. Kids will get hurt falling off their bikes, falling out of trees, diving into the shallow end of the pool, etc - to say nothing of the bigger-picture "life" risks of falling in with the wrong crowd, doing drugs, drinking, whatever other vices. I'd much rather have my child engaged in a team sport, even if it carries some degree of injury risk, and learning how to be part of a team, listening to a coach, the importance of being on time, winning, losing...all the stuff that Evolv mentioned.
I also think the risk of CTE is much, MUCH higher for guys that have played high-level Division I and NFL football than it is for the vast majority of middle-school and high-school kids playing ball. I was no shrinking violet on the field, but watching my tapes and comparing them to the hits doled out in NFL games...there is just no comparison. Most of us are just not strong and fast enough to deliver those kinds of crippling blows. I remember a small handful of hits that I felt were real slobberknockers from college, but even seeing those on tape later, they're nothing compared to what happens nearly every play in the NFL.