Core i3 is dual core, but with hyper-threading (a feature which allows one core to run two threads at once). Pentium processors are dual cores without this feature. Windows will see an i3 as a quad-core because of hyper-threading (though a hyper-threaded core isn't as good as two cores and two H-T cores isn't as good as four cores, it's better than cores without H-T)
What are you actually asking? i3 is a dual core processor, so no, it's not any better than a dual core processor. However, it might be better than a Intel Pentium G630 or a Athlon II dual core or a Phenom II dual core. It depends on what you compare it to.