there are quite a few issues, i'll put them in no paticular order. each section may be entirely different from the last, perhaps conflicting. hence different sections, different ideas.
note; basing this off of b5 play since i haven't played b6. but i doubt much of anything will be different, unless theres ninja nerfs.
as well, please note we base this game off of the supposed "top of the line" players, so skill isn't an issue, its expected, isn't it?
Hitboxes
As it stands, the hitboxes are the aliens saving grace. if the marines hit all the shots they fired at aliens, they would never stand a chance. Skulks die in less than 1 second vs a LMG, which you can see from time to time when the hitboxes don't crap out. other times, you'll unload the entire clip and hit nothing. hence, saving grace. if the devs were to fix the hitboxes, you would have to nerf the damage of the marines and increase health of basically every life form. onos is most noticeable when it comes to marine damage, due to the giant wall of a hitbox it has. hmgs solo onii with stupid ease, but have problems against fades blinking with celerity due to hitboxes. so, i'm kind of hoping hitboxes stay broken until the dev team realizes that marines are overpowered.
Marines In General
FAR. TOO. GOOD. sieges go up way too fast with more than 1 person building(its kind of slow with 1, but still very fast) for a no line-of-sight high-damage anti-structure freaking uber cannon of death. the fact that scanning allows the sieges to hit makes them way too powerful. most siege locations are very easy to hold, ala uturn. but actually going into the hive, the marines get destroyed. so they siege, and can't be touched. this isn't really fun for anyone. if its just the hive, its a "net loss" in res cost for marines(40 for hive vs 25 for tf + 15 per siege, assuming more than 1 siege, and a pg is there) but the 3 minute downtime and lack of an ability+chamber really, really hurts aliens. siege needs to really go. unless the marines overall utility gets nerfed, that is.
Marine's weapons are insane. drop an armory, you can drop shotguns. WHY. shotguns are INSANE for a no-upgrade weapon. they do better than the 15 res upgraded armory gls vs hives, which is supposed to be the structure counter weapon(right?). sgs deal hundreds of damage PER SHOT at close range, but "suck at range" so its "okay." no. aliens are pure melee, this counters their entire freaking existance. then they do full vs any structure, including hives. which allows marines to drop sgs, get a pg next to a hive, and drop it before the "hive under attack" message plays(literally). it also allows marines to drop onii very easily, as well. counters redemption entirely, on a 75 res lifeform, because of the threshold(has to be no armor, <~330h, sgs can do that like its a joke).
on top of it all, marines can get armor3 quickly. the base damage is beyond enough, and armor3 just makes it stupid. 4 hits is a LOT considering the DPS of marines. lerks take even more bites than that, and are already paper. spore needs to eat armor more, to make this strategy no where near as effective. as it stands, i've rushed armor3 in pubs and not lost without killing one fade, due to the fact that my marines DO NOT DIE. 4 hits is way too long for a fade to stick around vs any weapon.
overall, marines = far too much utility. they get the end of every counter chain, and have things that have no counter chain at all.
conclusion for me? marines = overpowered. way too much utility compared to aliens. aliens require hive2, marines are just good the entire game.
Hive abils
hive 2 is great. bile bomb, metabolize, leap, umbra, stomp. great abilities, aliens absolutely need these to hold a candle to decent marines. problem is, marines can drop hive2 or completly shut it down very, very quickly. 3 minutes to get a hive up, and provided aliens do not get mcs, marines can shut the aliens out of the hive entirely. if aliens get mcs they stand a chance, if friendly fire is on. even at that, marines walk in and drop the hive in 3 seconds.
hive3 is considered complete crap, usually because the game is over by when you get it. its also impossible to hold 3 hives in any real game situation(one marine brings many with a pg). primal scream and web are by far the best alien weapons. sadly, they never really get much use due to the hive holding situation. scream is sometimes used to kill the ips of the marines at the end, yay?
hives need a fix overall. need to be stronger, and have a better way of defending it as far as the aliens go. aliens should be very strong in the hive location. marines can hold their base with distress beacon, why do aliens get nothing of that sort?
phasegates
yes, pgs get their own section. one marine can build a phasegate. why? its so easy for one person to get into a hive and get one of these up. they build so quickly. then the commander can just beacon, drop weapons, marines phase in, get ammo from comm there, hive is dead before aliens can turn around in the direction of the hive. is it the aliens fault for letting ONE MARINE get past? you can't seriously ask aliens to check every corner, i mean, aliens are supposed to be the ambushers, and marines use teamwork. i see no team work in one marine building a pg. thats literally rambo right there.
pgs also allow marines to hold any position on the map with ease. aliens get no such grace, they get MCs. which allows them to hold pre-set map positions, provided the hive is either active or under attack. oh the hive is dying, let me mc in! *use mc* *dies to sg before turning 45 degrees*
jetpacks
okay, these things are just stupid. they allow marines to chase down any life form and get anywhere on the map with stupid freaking speed. no, the weapons do not weigh marines down nearly enough. then they're STOMP IMMUNE? if the jp is ont he ground, he should be treated as a regular marine, because hes given up the jp advantage, or is finally out of fuel(which is when they should be regular marines, so aliens can hold a candle to jps). if a lerk wants to fight a jp thats a whole different story. first, they have to predict where the marine is going and hope to god he doesn't change directions. then, if he does, they have to turn and flap a ton to gain speed(current flight system is crpa, adj seems to be working towards a better one though) and its just overall crap for lerks vs jps. gorges are the only real counter to jps, with HIVE 3 WEBS. oh you don't have hive3? oh well.
motion tracking
remove this. no reason for this to be in, with the rest of what marines get. give obs mt in range, or something, at most. this is far too powerful. counters skulks entirely, and removes any chance of aliens getting any location held. the marines can get anywhere long before aliens. if you don't see why mt is overpowered, you aren't playing ns, honestly. it just counters the entire alien idea. allows marines to track and kill fades with such ease. same for onii, or any lifeform. then you can add this to jetpacks. or marine "ninjas" who get that phasegate in the hive(they can see where to hide based on where aliens are moving, etc)
my conclusion
marines are overpowered at a ridiculous level. their entire tech tree is insane. hitboxes are the aliens SAVING GRACE? WHAT THE HELL. winning should not be reliant on a netcode. marines can ninja, sgs deal full to hives. so many things wrong, so much time to fix them. so get to it, please. this game has so much potential to be fun, it can be balanced with effort. i haven't seen a balance change since 3.0.
Marines = need nerfs
Aliens = need many, many boosts, or an extreme marine nerf to bring them to their level.
edits:
Shotguns
See: all other sections.
Fades
Fade is an interesting class. depending on luck, and the player, it can turn the game around. its absolutely needed to hold hive2, though. the "hit and run" unit of aliens. funny that every other alien has to do that too, though.
Onos
Hitbox is too large for marines dps compared to its HP. supposed to be able to take on a few marines, but it can't take on ONE HMG? needs a lot of work. sticking with my "nerf marines" theory, upping it at all would make it useful vs lmgs.
Distress Beacon
worst idea. ever. sorry, recalling the entire team to a specific spot for 15 res isn't fair for aliens. especially when it can be done from anywhere on the map. if aliens "lame it up", then yes, for 80+ res, you can hold it for a bit. but marines will overpower the ocs easily. then marines can phase instantly after being beaconed? need a no-phase timer in there somewhere.. should be used for getting a dead team alive, not rofl-owning a hive.