Well obviously, on the technical side of things, these guys are unmatched. But, there's of course a reason why they're mainly known and admired within the musicians (specifally shredders) community
People don't really want to listen to them, because it technical, and theoritical, and there's no lyrics.
They're amazing guitarists to be sure, but not great ones. Ain't none of these guys Vaughan or Clapton. But they're all bloody brilliant to be sure
Malmsteen is easy to dismiss as a weird nordic shredder with bad outfits, but man oh man. I've studied music theory quite intensely for a few years, and this guy is pretty much as schooled as they come. I have several of his DVD's, and listening to him talk about how he puts his music together is like listening to a lecture on the half cadence. Most people find it dull, it interests the hell out of me. Plus he plays a scalloped strat, that's just cool
Vai is like a freakin' institution among guitar players. He's brilliant, melodic, and he has some pretty serious chops

Technically speaking, he's probably the best guitarist I've ever seen. The fluidity of his hands...boy it's a sight to see. He has some great music though. Bad Horsie, Blood and Glory, The Attitude Song, For The Love of God. These are pretty much melodic shred. Like listening to Mozart, but with an Ibanez and an effects pedal
Satriani? What can you say about Satriani. Surfing with the Alien is a classic, and any guitarists would laugh you out of the room if you didn't at least know the title track. He's a great writer, he wrote some classic columns a while back, and he tutored Vai and Hammet

What more do you need? Plus he does that two handed tapping thing. And his guitar is chrome. Cool