I'm wondering if ME3 is like ME2. All encounters are pretty much close or medium range, so the sniper is pretty much unused during the game.
So is it good to carry the ME3 sniper around? I'm asking because they are heavy and I would need this extra reload time on my abilities.
If you're an Infiltrator or Soldier you get a "time dilation" effect with the sniper rifle which slows down time. Soldiers have to use the Adrenaline Rush ability to slow down time which can allow you to take a careful headshot or two, Infiltrators actually get a passive slowdown every time when you're scoping with a Sniper Rifle.
The slowed time allows you to take headshots easier, in addition these classes have a high weight allowance, so carrying around Sniper Rifles isn't as detremental to your cooldown.
Infiltrators get additional benefits for Sniper Rifles, as their Operational Mastery skill increases the sniper damage and time dilation effects at certain levels. Tactical Cloak also allows you to take your time to get a good headshot while dealing extra damage to boot.
You'll never really be at extreme range, but the extra damage a sniper does comes in handy if you can headshot a humanoid foe. If you're not a good shot or you're not playing soldier or infiltrator you probably shouldn't bother with Sniper Rifles because of the weight issue you note.
As an infiltrator I try to position my squad mates closer to the front under cover and I back them up with the sniper rifle. Snipers really do a ridiculous amount of damage if statted properly and the melee bonuses on some of the infiltrator skills make for an interesting combination. Once you get the Black Widow 1 you'll probably be killing anything without major defenses in one shot.
The only real challenge with snipers is hitting moving targets and ammo conservation. If you get down to melee you're generally hitting F9 at that point...
Are you playing an Infiltrator or a Soldier? If so, you have the tools needed to make Sniper Rifles work for you. Infiltrators can use Tactical Cloak to position themselves strategically to take out opponents from long ranges, and line up a perfect shot unnoticed. Soldiers meanwhile, can use Sniper Rifles to open an engagement, as well as shooting from the hip with them to get a little bit of extra punch against armored opponents.
Keep in mind, Sniper Rifles are still quite good, even at fairly short ranges, because they allow for a great deal of precision when you fire, have high armor penetration, and time dilation makes it easy to line up headshots against small targets like the soft points on Brutes and Guardians.
Playing anything else? The added weight is probably not worth it - without the time dilation benefit that Soldiers and Infiltrators can gain, it's difficult to line up a shot on a moving target under fire - getting off one round isn't worth the additional recharge time to a Vanguard, Adept, Engineer or Sentinel.
I'd just like to add that even if you aren't a Soldier or Infiltrator, if you know you're going to be going up against an Atlas, you'll want a sniper rifle to deal with one as its the easiest way.
A powerful sniper rifle with a high rate of fire and the time dilation effect makes you almost unstoppable. For example, my current M-29 Incisor II allows me to carry 138 bullet and it fires 3 bullets at a time, combine it with time dilation to make headshots easier and you can take out most enemies in one pull of the trigger. Every time you pull up your scope time slows down so you can easy pick them off one-by-one.
Time dilation on Soldiers and Infiltrator make sniping a viable option, especially against heavily-armored enemies. They provide the most burst damage against armor. Snipers like the Widow and Javelin are tremendously powerful, and will allow you to one-shot enemies like Marauders, Centurions, and Geth Rocket Troopers from full shields, provided you have stacked damage on your Adrenaline Rush or Tactical Cloak.
Aside from that, it makes thin cover almost irrelevant with AP Ammo/Pierce Mod/Javelin/Widow/B.Widow.
The rifle in question is a factor as well. The effective range, power & weight vary significantly between all models, even before you factor in modifications or upgrades. My personal favorite is the M-13 Raptor. It's high, semi-auto rate of fire & generous ammo capacity bear more resemblance to a light rifle (similar to The BR-55 or DMR rifles from Halo) than to some of the more traditional "bolt action" sniper models. Send me into the field with that & a Scorpion pistol & I need nothing else.
