Sicilian's Are NOT OP

***This is my opinion for playing the Sicilians in the lower ELO ranges. (650-750 personally)***

If you play as the Sicilians, you will quickly find where they fall short. Here is what advice I'd give anyone who struggles against them in the lower ranked queue's:

1. Serjants are slow. It's pretty easy to avoid fights with them.
2. Counter raiding will be more effective if you can push them off stone or gold. Using quick walls and defensive towers at home until you have your upgrades.
3. Donjon's can be battered down if they dont have Serjants babysitting them. You can get quite a few vills around the base. This keeps the Serjants within range of the Donjon's, or they risk losing substantial resources.
4. Scout wide, try to spot the vills going forward to drop the first Donjon right around the time they go up to feudal and batter it down with your own vills. They likely wont have the resources for another forward drop.
5. Get armor upgrades before engaging Serjants with militia line units. Serjants do less damage, but have more armor, and cut all bonus damage received in half. Don't use ranged units right off the bat unless you 100% kite them with micro. Serjants have 1 melee/2 pierce armor in feudal, and 3/3 automatically in castle. Use melee units, get your upgrades before engaging, create them while getting upgrades.
6. Try to apply as much raw melee, or pierce damage as possible to any kind of land unit. Do not rely on typical counters that have bonus damage, they only apply half of their bonus. MAA do more nearly the same damage to their scouts as spearmen. Coming out to (at most depending on damage rounding) .5 DPS less while upgraded. (if DPS rounds down, it comes out to .167 less when upgraded). And the extra pierce armor of the MAA helps out if you are going to fight under a Donjon.
7. There is not much room for error on the economy for supporting early aggression. Disrupting wood, stone or gold hinders the building of Donjon's, or spawning of Serjants. (Not saying its ok, but laming REALLY hurts)

TL:DR Losing to a civ you don't know how to counter might make it feel OP, and while there might be some balance tweaks coming, I wouldn't count on them being very aggressive. Play with them, see for yourself where their challenges are, and put pressure there when you go against them.

EDIT: First Crusade does need a bit more balance, I could see it being more expensive, and going from 10 out of 5 TC's, it does 5 out of 10 TC's. Still helps with countering a raid, but requires much more investment into the TC's if you want to quickly raise an Army. It currently costs 20% (at least I think so) of what it takes to build those same units in a castle or Donjon. That seems pretty low, and needs either a cost increase, or a long term consequence for using it. Like decreasing their future build speed in castles, to Donjon speeds.