One problem I have with Calvinism is that it seems in constant conflict with the doctrine of Perspicuity, which I contend is a very important doctrine to keep in mind. While the Bible is not always easy to understand, it does speak plainly. God isn't playing mind games with us, saying one thing but meaning another. Thus, it is a basic principle of hermeneutics that the clear is used to interpret the unclear. If, for example, you have a verse that says "baptism now saves you", it must be interpreted in light of the multiple other verses that clearly tell us we are saved by grace, through faith, not of works.
Now, in my mind, the clarity of a verse can be determined by how much it needs to be explained. Parables aren't clear because, by definition, they require explanation. But the explanations themselves don't leave much to the imagination. Can you explain the parables of the sower, or the prodigal son, or of the good Samaritan, better than Christ Himself did? Good luck with that.
Here's the reason I believe Calvinism conflicts with Perspicuity. Scripture clearly tells us that God takes no pleasure in the death of the wicked, that He isn't willing that any should perish, that He wants all men to be saved, etc. When confronted with these verses, Calvinists tend to have two responses: Add words, or change the normal meanings of words without justification. At least, without justification beyond "if we take the normal meaning, Calvinism is wrong, but if we change the meaning, Calvinism is no longer threatened".
Tell me, how clear is a verse if it needs you to add words to it? Take, for example, when 1 Timothy 2:4 says God wants all men to be saved, and Calvinists change it to mean God wants all categories of men to be saved? In my eyes, 1 Timothy 2:1-7 is pretty clear. I don't think it needs adding to. God did a rather good job inspiring it, and I'm not sure He'd be pleased if I messed with it in any way. Yet, Calvinists need to. Why? So it fits their doctrines.
In reality, it seems to be the verses Calvinists favor that are less clear. Not that they can't be grasped with prayerful and diligent study, but that they require this prayerful and diligent study indeed. We all know how Calvinists love Romans 8-9 in particular, often simply name dropping it as if that ends the discussion on the spot. Yet, I'm sure a skilled preacher could make a whole sermon out of almost every verse, there's that much to unpack. The passage is not as simplistic as Calvinists make it out to be. The passage even requires the reader to turn back to other Scriptures to ascertain its meaning.
There is a saying: "All means all, and that's all all means." 1 Timothy 2:4, therefore, is one of many clear verses that ultimately make Calvinism unworkable. Romans 8-9 is a passage that needs to be studied in light of it. If this means rejecting Calvinism, the honest student of Scripture must declare "so be it. To God be the glory."