Hmm, I tried the "demo" of Risky's Revenge. The lack of difficulty and the plane switching mechanic makes traversing the 2D stages quite confusing. It's definitely a good game for a more casual tastes.They are very good and fun games. Very rewarding gameplay, cute looks and a great soundtrack. The difficulty is very fair if you are used to platformers.
It becomes more challenging in the later game but yes, they aren't the most difficult of platformers.