You need to understand how effects work. Time based effects dont sound good in front of distortion. Flange, chorus, delay, harmonizers. All there doing is creating another note thats a different pitch. What happens when you play 2 seperate notes at the same time on guitar? You get 2 notes distorted together. Delay is the same thing. A note repeats and at the same time youll be playing a different note and both notes get distorted together. Same with reverb. The distortion just distorts the reverb giving you a pretty nasty sound.
They work after distortion becouse the distorted signal is split, retuned and put together with the origional distorted signal.
Certian effects are cool in front of distortion. Octave harmonizers (it sounds almost the same as just playing an octave on guitar), Phasers (for an EVH sound), envelope filters (Wah, auto wah).
You can get a radical effects by putting those time based effects in front but its different from what the intended effect is. For instance if you put a slow chorus in front of distortion it sounds like youre playing slightly out of tune unison notes on your guitar. Its very creepy and Ive used it alot.
Listen to POD-Alive, at the "and now that I know you.....I can never...." part. Or Metallica-I Disappear at the "do you bury me when Im gone..." Thats pretty much the way a chorus or flange will sound in front of distortion. Despite whatever effects they may have actually used on those tracks.