Level 10 in melee is about where you can travel between villages safely. You need the hit points, self heal and a weapon better than the starting dagger. You may die at a much higher level if you get surprised after a tough fight, but by the mid-teens you can be fairly confident traveling if you watch out for agro mobs.
SoR is a skill based system doesn't and can't have the level based con system of other games. There are a few things gaining a level will help you with immediately, but for the most part you have to train and spend the skill points you gain for the benefits of a new level. A lot of difficulty depends on your equipment, specially starting out. Going from the starting dagger or amp to a player made quality 20 weapon or amp will make the ragus that was certain death into an easy fight. (Just watch out for his 3 friends, the ragus' special power is to summon his pack mates.)
There are six measures of difficulty in SoR:
1) Stars
2) Mob Names
3) Mob size - repeats in different zones
4) Color - based on zone, but there are some exceptions
5) Quality of mats the mob drops (sorry you have to kill one to see this)
6) Your experience
In each zone there are four types of each species which are assigned 1 to 5 stars. Some mobs may top out at 3 stars while the toughest of others will have 5 stars.
Each type of mob (carnivore, kitin, bird, etc.) will follow the same naming convention. See:
http://www.ballisticmystix.com/mobClassList.jsp or
http://ryzom.l9c.org/mobs.php?do=name When you move to the mainland, print one of these lists. They enable you to tell if something unfamiliar is a predator or prey.
The tougher a mob, the bigger it is. A 1 star blue Vigorous Kipee is the same size as a 1 star red Nettled Kipee.
The actual level of the mob is indicated by the level of mats it drops. The level determines how much experience you or your team gets.
You can use these indicators to judge the relative difficulty in a new area (hmm, the scary ragus is 1 star but the scary torbak is 2 star; moral if you almost die from the scary ragus, avoid the scrary torbak), but con is your own experience.
Hope this helps.