This wasn't my introduction to logic, but I like to skim it for refreshers, and it seems well-written enough to me.
My introduction was What is Mathematical Logic? by Crossley et al., which is a master class in terseness and probably more suitable for someone who's already got a foundation in logic. I must've read the first three chapters three times each, and the rest fewer times than I should've :-).
Superb writing and well motivated.