If you read the suggestions forums you'll notice that only bad ideas get a lot of replies, if your idea isn't bad, no one is going to bother replying to your thread unless they absolutely love your idea.

Too many possible combinations.
What would happen if 3/4 people charge at same time? wich combination has priority?

Shrink the spear, and have it fired by some electro-mechanical device. Perhaps turn it into an energy ball or the like rather than an actual spear.

There are 3 basic types of weapons. You have those that you attack with nice and close, those that attack at range, and those that are timed. What more do you need? A remote detonated bomb?

I can see a few problems with co-op charge attacks, primarily planning issues; I don't know what the ratio of mic-users to text-only chat users is, but you simply cannot coordinate via text in a busy fight. Players could potentially coordinate by reading their teammates' behaviour, for instance noting their angle if they're charging and working out where their attack's going to go, but [i]that[/i] comes with another issue - what if your well-intentioned combo attack messes up their planned approach? I dunno. Encouraging intra-party cooperation is a fine idea, but I don't know if this is how to go about it.

The friendly shielding is more intriguing, but potentially a bit overpowered. You get, say, two guys shielding, the other two shooting or bombing. You rotate shielders as their shields get close to breaking, so when one turns red, someone else steps in while the first dude's shield recharges. It could be really, really cool, but could also remove a lot of challenge, as the party would never really be in serious danger from enemy attacks. Perhaps, instead of directly shielding nearby teammates, overlapping shields could buff each other? That way, there'd be a palpable benefit from diving in to aid a beleaguered party member, but neither player would be able to attack whilst gaining this advantage, balancing it out some.