I can't speak to the original ECW as I've seen very little of it. But for a couple years WWECW was the only wrestling I would regularly watch, and not just watch but usually be excited to watch. After JBL left Smackdown, ECW was the only wrestling I was watching outside of goodhelmet comps probably right up until the time that CM Punk started his feud with Jeff Hardy.
I loved ECW because it was SIMPLE. They stayed focused on a few storylines, and had such a small roster that they had to keep everyone fairly strong. Even Stevie Richards had a win streak at one point. Plus it would probably have as much wrestling or more in 1 hour than Raw or iMPACT would have in 2. With a roster that at different points included: William Regal, Finlay, CM Punk, Evan Bourne, Christian, Matt Hardy, Mark Henry, Goldust, etc.
ECW was also great as a starting point for bringing new guys into the company. Guys who started on ECW and went on to success on Raw or Smackdown include: CM Punk, Sheamus, Kofi Kingston, Evan Bourne, Jack Swagger. It was also a big boost to careers of younger guys like John Morrison, Miz & Zack Ryder who were given time to develop characters that they probably wouldn't have gotten on Raw or Smackdown.
In closing, I still miss ECW and wish I was watching Drew McIntyre as ECW Champion instead of a part of 3MB.