A very good question.
Evangelicals believe in the centrality of the conversion or "born again" experience in receiving salvation, in the authority of the Bible as God's revelation to humanity, and in spreading the Christian message.
Evangelicals particularly emphasize "conversion experiences"
as an adult even for people raised in Christian families, and reject the authority of old Christian philosophy, particularly w.r.t. the ideas of Saint Thomas and Saint Augustine (although Thomism still pops up here and there), in preference to
de novo (and often questionable) interpretations of the Bible offered by modern priests.
I would generally advise Christians to avoid evangelical denominations for the same reason that I as a Buddhist generally prefer traditional (mostly Japanese) Mahayana Buddhist centers to New Age-y stuff like Shambhala. This is the core of the argument in Wittgenstein's
Remarks on Frazer's Golden Bough: "religion" is a sort of instinctual human-qua-animal activity, and the attempt to apply modern constructs like axiomatization (e.g. the Bible as the axioms of Christianity) and
critical philosophy (a fundamentally Enlightenment and historically Kantian idea, preoccupied with technicalities such as the free will paradox and the paradoxes of omnipotence) to religious ideas tends to lead to useless nonsense.
As such, one of the bad characteristics of Evangelicalism is that it tries too hard to be modern and ends up being ludicrous. The other bad characteristic is that "conversion experiences", while occasionally effective at changing behavior, can become culty indoctrination rituals, which can
cause plenty of problems in any religion no matter how noble or educated the membership may seem at first. Conversion experiences are much like psychedelic experiences: when offered by a corrupt "spiritualist", they can be extremely manipulative. The hostility of Evangelical Christianity towards traditional forms of church governance increases the risk of this kind of abuse, and there is now even
a counter-cult movement within the evangelical movement which has tried to counter the fallout of these conversion experiences propping up abusive "churches" and "Christian communities".
