I think a division has to be made between charismatic and pentecostal here. 'Charismatic' has never entailed anything other than the belief that spiritual gifts (tongues, prophecy, healing etc)are alive and kicking. Many Charismatic churches regrd themselves as reformed - indeed as Calvinist - including my own.
Pentecostal belief, as I understand it, is that unless you manifest spiritual gifts you are not saved - or, at least, that all christians will manifest those gifts. Obviously, this can be utterly innocuous - or it can be a grotesque violation of 'whosever believeth in me', depending on interpretation.
There are, obviously, a number of charismatic and pentecostal churches that are teaching some extremely unsound theology. I think that has more to do with the appeal of the 'experience' of Charismatic faith attracting people who have a poor biblical understanding than the other way round.
All the same, I do have to agree that sounder Charismatic churches, while they may not fall down on the teaching of the word, do fall down when it comes to individual member's own knowledge of it. I would certainly apply this to my own church. The teaching is excellent - and thoroughly reformed - but many people in it would have difficulty with biible knowledge beyond a basic plan of salvation.
Which is why heresy arises, of course.
Magi