Arminianism is an attractive school of thought. I find the tenets of Arminianism not to be as repulsive as many Calvinist attempt to make them out to be. I agree with the Calvinist on many things; the converse is also true. Likewise, I agree with the Arminian on many things, yet I disagree with them on a few as well.
My objection with Arminianism is that it does not account for a robust understanding of sovereignty. If God has merely two logical moments of knowledge (natural and free) then logically prior to God’s decree of creation he did not know what the world would be like. He could know all possible worlds prior to the decree but he would not know the actual world until logically-post his creative decree (via simple foreknowledge). William Lane Craig comments:
On such a view [no middle knowledge] of God [he has], logically prior to the divine decree, only natural knowledge of all possible scenarios but no knowledge of what would happen under any circumstances. Thus, logically posterior to the divine decree, God must consider himself extraordinarily lucky to find that this world happened to exist. “What a break!” we can imagine God’s saying to himself, “Herod and Pilate and all those people each reacted just perfectly!” Actually, the situation is much worse than that, for God had no idea whether Herod or Pilate or the Israelite nation or the Roman Empire would even exist posterior to the divine decree. Indeed, God must be astonished to find himself existing in a world, out of all the possible worlds he could have created, in which mankind falls into sin and God himself enters human history as a substitionary sacrificial offering! [Anthropomorphically speaking] 
The Calvinist recognizes the problem as well—his solution, though, is to implement determinism. However, the events in history are not by mere happenstance (Is. 46.9-10; Eph. 1.10; 3.9, 11; 2 Tim. 1.9-10). Yes, God will be interacting by means of providing grace and revelation to control his creation, but I don’t find this to be as robust of an understanding of sovereignty as the Molinist’s understanding. Determinism doesn’t work for theological and philosophical reasons I’ve previously discussed. If God does have exhaustive knowledge, including a second [of three] moment, middle knowledge, then God knows all possible and feasible worlds (and the actual world).
 I know Arminius attempts to use middle knowledge but it’s not the same understanding that Molina implements. Unfortunately, I don’t have my library with me at the time to elaborate and cite the issue.
 William Lane Craig, What Does God Know? Reconciling Divine Foreknowledge and Human Freedom (Norcross, GA: RZIM, 2002), 50.
 I want to note that simple foreknowledge lies within the third moment of God’s knowledge, not his middle knowledge.