The student in my class who has started using it said there is a learning curve, as with everything, but is not particularly difficult to figure out.
The second online game creator is called Sploder. This site offers the opportunity to create flash games to play right on your PC. I personally played around with it bit, and I must say that it is pretty cool. The site provides many options for character develpment, background, etc. Sploder does however regquire users to register. So if you have younger students who are interested, parents or teachers could provide their email address. This option might be useful in that he/she would then know that students password and username.