History is full of 'looks cool but failed' weapons. The Discovery presents these things in a light that glosses over many of the impracticalities. For example, Metal Storm has an incredible rate of fire - it can empty itself in a couple of seconds tops. So.....how easy is it to reload? Do all soldiers carry prefab rods of ammo around? What about reloading the larger version? Sometimes, rate of fire can work against you, especially for reload/resupply.
Aerial or ground-based lasers - I really won't argue that lasers, and other directed energy weapons may well be the future, but any physics student can tell you of the weaknesses of light, especially coherent light - it can be diffracted and refracted - does it work during a rainstorm, when each water droplet could split or bend part of the beam? Recharge rates for chemical lasers are also a problem, and the power pack for other systems is currently bulky. The Israeli's have had some success with their Tactical High Energy Laser (THEL) system, but I'm not sure how far away from fielding it is. There is something to be said though, for being able to drill a hole into somebody's skull from a long distance.
Rail guns - they create an immense transfer of kinetic energy to their projectile, but the wear and tear on the barrels so far has limited them to experimental status.
MLRS - can be very precise, good range, lots of submunition types available - tried and accepted system. I would wonder though, whether pound for pound of warhead delivery, is a conventional arty round, the howitzer, and crew, a cheaper alternative? The M777 can be very accurate, has a good range for anything we're involved in, and is probably a lot cheaper to operate in terms of delivering the same amount of high explosive onto a target.
EMP Blast - now that's damage without killing folk off. But, I think it was General Giap (?) of the NVA is famous for saying 'the Americans threatened to bomb us back to the stone age, but we were already there" (or close to it - might be wrong on the attribution). A low tech force won't be overwhelmed by such a device (i.e. the Taliban - though it'd screw up their use of cell phones for comms).
If you want to scare the crap out of yourself with a weapon - think enhanced weaponized Smallpox. Most males of military age in CA and the USA haven't had the shots, or their vaccination was for a specific strain no longer in existence.....