Imperium Universalis is absolutely massive and, thus, suffers from performance issues. The game ranges from Spain to China, Denmark to Nubia. There are many, many, many provinces and tags.
Although it is a classical era game, it is still very much EU IV like. The main focus is on conquering territories, increasing your technology and navigating the diplomatic landscape.
Neither is better or worse, they are quite different games. I:T is much tighter and smaller in scope, Imperium is much looser and larger in scope. If you like the warring and diplomatic aspect of EU IV, you will really enjoy Imperium.