A sim often overlooked for helo combat simulation is Operation Flashpoint. The physics are poor compared to most helo sims, but considerably better than arcade flying. The basic controls are there: collective, cyclic, and tail rotor. But the helos are autostabilized, so flying them is fairly easy.
Where OFP really shines is the operations and immersion. Mission design in OFP permits very complex and realistic missions including transport, SAR, and gunship duties. If you are playing online with many people, a good helo pilot can make a big difference in the ground fight but are also nearly as vulnerable to ground fire as in reality. Name another helo sim where you can land, hop out, get into some firefights with your M-16, and jump back in to fly home
It is literally a blast to engage targets with large numbers of unguided rockets. Unfortunately, unless you have a real person acting as the gunner, targeting with guns is a little difficult.
There are so many addons available that you can fly just about any helo you like. Helos can even be used to move light vehicles by cable. If you get good at scripting missions, just about anything is possible.
Of course, within the next year or so, Armed Assault should be released (the followon to OFP/Resistance... OFP 1.5). I think it is supposed to make some improvements in the flying physics, but I am not holding my breath.
