Hi Well i my SCJP exams are on saturday so i am yet to compare it's level of difficulty! But a friend of mine that has taken and passed says u really have to hit 100% (just as it says on the site..) so as to know u r ready.. U have to because it tests the basics of the exams... So if u cant get 100 on the basics then something is wrong with ur basics.. I have hit 100% twice and an average of 85% on all the questions.. Well it doesnt really mean u have to get it all ! Anyways just read with the mock sites and also try out www.javacertificate.com it's also really lovely.. Saheed. SCJP 1.4(coming sat..) Imagination is better than Knowledge..
I wrote both the original Rule Roundup Game and was one of the developers of the real SCJP, so I can tell you that the questions on the Roundup Game are NOT like the real exam. The Rule Roundup is meant to help you memorize the basic rules, which you do need to know before taking the exam. But in the real exam, most of the questions are more involved, and more difficult and they do not usually ask you about the rules but instead expect you to *use* your knowledge of the rules to solve a problem or figure something out.
So, you should be getting close to 100% on Rule Roundup Game, but even if you *do*, that will not tell you if you are ready for the exam. You really do need to do some good mock exams--there are plenty available for you online.