I intend to use Crossbow as a sniper weapon since that is what they are designed for. Aim like a gun and good damage but long reload time so distance is key with that weapon.
Crossbows lose accuracy badly. They are powerful point blank weapons. Historically, their value was that they were easy to use and could therefore be given to relatively untrained troops. Good longbow archers OTOH took years to develop.
I think that they are a great addition to Skyrim. First, they should be the standard ranged weapon of guards and bandits - who I see as ill trained. Second, they make a great addition to the warrior class - fire a crossbow and then charge. No worries about noise or reload time because you are only taking one shot and you are not trying to be sneaky about it. This is where the extra punch of a crossbow should serve a player well.
As has already been pointed out, they are horrible stealth weapons. Short ranged, slow, and noisy. If you want to compare them with guns think shotgun with buckshot, not sniper's rifle.
