well a mass-effect-weapon is in fact just a highly advanced railgun/coilgun (it uses mass effect fields instead of rails/coils but otherwise it does the same: accelerate a projectile to high speeds (higher then old-fashioned firearms)...that's why the military today works on such weapons...if you had a working ME-Type-Gun, they would make you wealthiest person alive if you gave it to them...or they would kill you for it, that's cheaper after all ^^)
but the rest of your posting:
yeah - i always woundered why with all that technology their armor-suits were not more advanced (jetpack as mentioned, stealth (not just for certain people) if you want it (and can afford it - which Sheppard surely can...as can the N7-Programm, they are special forces after all), servo-motor-joints and heavy plating (while staying mobile because of the servos) that give you more agility, speed and power (wrestling a Krogan should be no problem in a suit of powered armor) etc.
hell we know that combat-exoskeletons are being developped right at this moment (the end product will probably look like Fallout Power-Armor)
same for weapons: if you have laser-ciws-systems, why not develop bigger systems (even more if you know that kinetic-barriers do not work on lasers)? - and again: humanity is working on laser-guns right now (!) and there are other examples of lasers in ME (in ME1 we had a quite large MINING-LASER...i would have loved mounting a few of those onto the normandy and focusing their beams more
then: how comes no ships in ME have internal defenses (from barriers and automatic-turrets to robots)? (boarding the normandy should not have been that easy in ME2 - for the collectors i mean)
well i'll stop here, otherwise i will write for pages on end ^^
greetings LAX