That's because I've been at writing for at least a year now, and have learnt a lot about writing. Only have the one fic anyways (well, two, one going to be released soon-ish after betaing of it is done), and the fic as it is now (especially the first few chapters) are better then what they were originally. Still, good to hear they're still enjoyable. :)
Just keep at practising the writing, and widen your knowledge by reading other fics (and reviews too, I guess). Entertaining to do and you learn as well!