Ibn Taymiyya's positions are more specific than the label of a hardliner suggests, and several of them cut against the reputation.
On God he held that the attributes named in scripture are to be affirmed as they are given, without allegorical reinterpretation and without asking how, and he attacked the speculative theology of the Ashari school for reasoning about God from premises it had taken from philosophy. He wrote an extended refutation of Aristotelian logic, arguing that the syllogism cannot deliver certainty about the world and that the definition by essence does no work.
On practice, his best known rulings concern tombs. He held that travelling to a grave for intercession, seeking a need from a buried saint, and building over graves compromise the exclusive claim of God, and he applied this to shrines of great prestige, which is what made it intolerable to his contemporaries.
On the Mongols, who had professed Islam but governed by their own law, he issued rulings that a ruler in that position could be fought, which is the single text of his most quoted in the twentieth century.
He also held positions that sit awkwardly with his later admirers. He argued that the punishment of hell may not be everlasting, a view he was attacked for in his lifetime. And his opposition to Ibn Arabi's doctrine of the unity of being did not extend to Sufism as such: he was affiliated with the Qadiri tradition and wrote approvingly of disciplined mystical practice. He died in the citadel of Damascus in 1328, months after his writing materials were taken from him.