I have used a Reegar II, and though amazingly fun to use and quite powerful, as many already mentioned the range is very very very short and it goes through ammo very quickly. It's great on an Infiltrator who can sneak in close, or maybe a Krogan who can wade through a lot of damage, but it isn't a versatile weapon. Oh and like others said, it does crap to armor.....i hear the shredder mod helps though.
As for the Krysae, isn't it almost just a sniper version of a Flacon or Saber?
Albeit the Falcon blows, and the Krysae is probably decent.
But yeah, probably in the future try them out before you pass judgement, i don't think you will think the are overpowered then.
You have to realize that most people are just using them because they are new, and it may seem like the players using them make them seem overpowered, but more likely they are just good players.
I have played with people using the Reegar and they did terribad.
And as for the Krysae, how is it any better than a Javelin or Widow or Kishock? It doesn't share there special traits like penetration or ability to ignore armor or 2.5 headshot multiplyer.
Personally I hate my Kishock 5, but in theory it's ability to ignore armor, no hip fire penalty, and 2.5 headshot multiplyer would make it an excellent weapon.