Pardon me, I know I've said it before, but ESB is a truly amazing style of beer. It's not that it's amazing or notable for any particular thing, but the beauty is in its complexity.
The name alone suggests something like an IPA... but it's not meant to be all-hops intensity. It's better-balanaced than that.
It has maltiness to it that is pleasing to those who prefer darker beers- this is especially true of the more americanized versions.
It is somewhat light, for the people who don't like to be weighed down by a heavy-tasting brew.
It is high-ish in alcohol for the people who demand something overproof.
It really is a jack-of-all trades in terms of style. As for Fuller's, it's a tad too bitter for my taste, but very good for a british-style bitter. I like more of the estery flavors and a hint of sweetness.