And too few great ones?
I know there are a lot of weapons that can be useful in the right hands and with the right builds etc, but they still pale in comparison to a few of the staples.
To me the best weapons in the game are:
Assault rifles: Harrier, Typhoon. Everything else seems underwhelming. Yeah there are some good other ones to use but really are there any that are actually better and more worth while to take with you than those two? Unless weight is an issue but in that case you are probably using your powers more anyways and the weapon is secondary to that. Maybe the Lancer gets an honourable mention here but after using it, I was totally underwhelmed. Don't even get me started on the Spitfire, what a useless POS that is.
Pistols: For me there is just no reason to bring anything else with me but an Acolyte. It's got to be the best sidearm in the game in terms of quickly dismantling shields to then use a power (or another weapon that is good against armour). I just don't see the reason to bring any other pistol except for the rare time I want to use the Scorpion for fun.
SMG: Hurricane, again there simply doesn't seem to be a good reason to use anything else in the SMG class.
Sniper Rifle: Black Widow, Javelin. Let's face it the rest of them are just underwhelming and while you can get them to work pretty decently (I like trying the Indra from time to time) they are just in no way on the same level in terms of killing efficiency.
Shotguns: I prefer the Geth Plasma shotgun, but I know the Claymore is popular. The wraith is also pretty decent but the rest of them? I never even touch, again due to killing inefficiency.
So while I know that there are plenty of viable weapons, there just doesn't seem to be much of a reason to use them unless you are going for challenges, or just trying to have fun with a different weapon. It would have been great to have seen a few more excellent weapons and not so many "just ok" ones.
I just feel like I am gimping myself if I don't take any of the aforementioned weapons with me.
TL:DR
Not enough "great" weapons to choose from. Too many mediocre/bad weapons.
EDIT: Just like to clarify that I know there are quite a few good weapons I didn't list here, but I feel that in general there are too many weapons in this game that are not up to par with the ones I mentioned, as well as some others.
AR: Add PPR, Saber in good ARs
SMG: Collector SMG is pretty good. Also, hornet is decent if you don't mind breaking your trigger finger.
Pistols: Paladin, Arc pistol, Executioner, Talon, Eagle
Sniper Rifle: Kishok, CSR, Indra, Valiant. Mantis and Widow are hardly useless
Shotgun: Venom, crusader, reetard carbine, raider, Graal
I might actually have missed other good wepons. Anyway
TLDR: You are a newbie and need to learn to play the game rather than complain.