The answer is that it depends on the class.
I just recently graduated this last spring and took about 80% of my degree courses online.
Having taken this many classes, I feel that I could give a person a good idea about how difficult college online classes can be.
The first thing that a person needs to consider that will directly effect the difficulty of these classes is the type of major they have selected.
What I mean by this is that a medical degree will have much harder online classes than a marketing degree.
If you are in an extremely aggressive and intense field of study, be prepared for some very difficult online college courses that will really take you to the brink.
The next thing to think about is what does the class material consist of.
All of us who have gone to some amount of college know that there are classes that actually teach you something and there are classes that are just fillers to get you credits.
The filler type classes are very easy to accomplish on line, but the classes that actually teach you something can be more difficult.
For example, math classes are designed to teach you methods, formulas, etc.
This type of class will be much more difficult to take online as opposed to a class designed around building your own website.
If you feel that you will need instructor help for a certain class or subject, do not take the class online.
Instructors are extremely limited in their ability to help a student when the class is taken online.
If you need one on one help in a certain subject, your best chance of passing the class is actually taking it in person and attending a classroom where you can get the one on one help you require to pass the class.