I am going to have to disagree with your statement and i will fully accept that alot of what makes a weapon so good is the skill of the user. Here is my manifest link
http://social.biowar...lay=multiplayerSo you can see what i have and do not have. I will also admit that i have a few holes and some weapons that need upgrading the M-99 is my greatest score to date next to my first Asari who is an adept class. So when i say what i am about to say it is entirely based upon what i have access to and the ability to demonstrate proficiency with the weapon, user results may vary.
I use a M-99 and IMHO it is the best weapon i have used to date. I have the reach and the accuracy of a sniper with out the narrowing of my view as with a scoped sniper. I have the ability to stagger most targets including phantoms. Nothing more satisfying than turning a Geth Pyro off mid flame as i slap that melon around. Nothing more satisfying than reaching out across the map and one shotting a cannibal, and his 5 or 6 buddies in tow, knowing that the other cannibals will stop in the shot attempting to armor up. The weapon is a bit on the heavy side but my Asari Adept carries one and i am in the blue 33% weight wise so long as i only carry it i get a bonus time to my powers. I have 8 rounds and each one is more than most targets can handle. I get 5 full clips in each load out for a total or 40 rounds. On average it is about 20 kills per load out.
The way this weapon works to greatest effect is fire from cover your accuracy is greater not much difference there. The first round just has to be centermass for the stagger efect, or in the case of a centurion the stagger roll effect. The second round to the melon and you need a new enemy because i just broke the last one. Plus as a bonus the weapon when fired sounds like a grenade just went off next to your ear. The BANG sheeeeeeeegooonk as the action cycles, means something just died.
I realize my opinion may change as i unlock more weapons in the future but even wityh everything i have in my manifest, and some of it is really cool stuff, i still love my reliable hard hitting accurate dealer of death so while i waited for almost 3 weeks to get my first Asari, Bioware did me a solid by allowing me to get one of these weapons early.
M-99 FTW, anything less any you might not make it out alive.

M-99, when you absolutely positively have to kill every MFer on the map accept no substitutes.