Anyway, infilitrator was my favorite class in the first, and will be my first playthrough in this one, it looks like.
Looks like the cloak isn't the only thing the Infiltrator has up its sleeve:
What makes the infiltrator the class best sniper class are his Tactical Cloak and Operative powers. We've already discussed how cloak lets you line up perfect headshots. Operative improves your weapon damage, and also adds a time slowdown effect whenever you are aiming your sniper rifle. This makes it easy to line up headshots, even against moving enemies. Combined with the damage boost from Tactical Cloak, infiltrators are without question the ultimate snipers.
You're taking the term "ammo" too literally. In the ME fiction the (non heavy weapon) guns still operate off the whole "mass accelerator fires grain sized pellets from a block of metal" principle as in the first game. In ME2 they changed how HEAT MANAGEMENT works to make the game feel more like other shooters with conventional weaponry without completely retconning how guns work in the ME universe. That's why they're calledthermal clips.
I had a little more patience with the story of this than most, I was OK with most of the weird supernatural stuff. But then they introduced the "Purple Clan". The fuckin' Purple Clan. Seriously, WHAT THE FUCK!