It has been argued by some Calvinists that the assertion "God is love" can be true even if there are people that God does not love. That sounds very odd so allow me to explain the thinking.
The statement "God is love" is rightly taken as referring to God's essential, necessary being. Within the Godhead there is mutual divine love between the Persons of the Trinity - the Father loves the Son and the Spirit, the Son loves the Father and the Spirit, the Spirit loves the Father and the Son. Thus "God is love" is a truth even if God does not create a universe containing beings for him to love.
But some in the Reformed tradition go further. They argue that if God freely chooses to create the world (and he did not have to create this world or indeed any world) then God is totally free to decide whether or not he loves everything or anything in that world without his choice impacting the truth of the claim that "God is love". Why? Because the truth of the claim that "God is love" depends on the love within the Trinity and so God's decision whether or not to love his creatures has no bearing on that truth whatsoever! Consequently it would be true that "God is love" even if God chose to hate every single creature that he created!
This line of reasoning opens the way for some Calvinists to feel reasonable when maintaining both (a) that "God is love" and (b) that God loves only some people with a robust, redeeming love (he only loves the rest with a lesser, non-redeeming love shown in common grace). It is true, we are told, that "God is love" even though God chooses to send some people to eternal, conscious torment when he could just as easily have saved them from Hell.
Here is what I think about that: It is both completely right and completerly wrong - and in that order.
It is completely correct in maintaining that God's love is an essential divine characteristic because it is grounded in the mutual love of the Persons within the Godhead. It is consequently completely correct to claim that the assertion that "God is love" is true even if nothing at all existed apart from God. So far so good.
It is completely wrong, so I think, to assert that God's essential nature of love would not be compromised if God failed to love his creatures. That would be to maintain that the following two propositions were fully compatible
1. God is essentially loving (in other words, it is God's nature to love)
2. God does not love some of the creatures that he has made.
But at face value that seems a very odd claim indeed. It seems much more 'obvious' to me that
if God is essentially loving then
3. if only God exists then God will love himself
4. if God has created a universe then God will love himself and the creatures that he has created
If God creates a universe yet only loves himself and not his creatures could we say that it is God's nature to love? That love is essential to God? Could we maintain with integrity that "God is love"? When pondering that question remember that the phrase "God is love" comes from 1 John and in that letter it is not God's self-love that is in view but his love for creation.
As an aside, I do not hear many Calvinists arguing that for God to be essentially truthful all that is required is that he is truthful within the Trinity but that he can lie through his teeth when speaking to his creatures. If God is essentially truthful then he does not lie to anyone. Well, the same goes (or so I maintain) with his love.
I would be interested to know what Calvinists made of my continued suspicion that propositions 1 and 2 above really are incoherent and that, consequently, traditional Calvinism really does have a serious problem holding on to the central Christian conviction that "God is love".