It's a given that the early FF and Spiderman hold up well, but I was surprised to see that Daredevil fares well. Having only read one of these early issues(number 8 with Stiltman), I didn't have the highest expectations. Maybe it was just because I've been so comic deprived these past couple months in college, but it didn't take long for me to see things through Matt Murdock's...eyes.
The early issues with Joe Orlando hold their own, but when Wally Wood comes around with Sub-mariner it gets even better. John Romita's first appearance in issue 12 with Ka-zar also improves upon his predecessor. There is nothing here that is going to take your breath away, but if villains such as the Owl, Gladiator, Electro, and the Fixer give you a warm fuzzy feeling, or at least some sort of memory, you need to have this. If you haven't really experienced the silver age of comics yet, you're probably better off starting with ol' Spidey and the FF first.
The major problem I have with these early issues is not so much the lack of originality or redundancy, it's the cliche love triangle and occasional inconsistencies. The first 3 issues show promise, with Matt aloof and uninterested in Karen's feelings towards him. But in the next issue, Stan Lee decides to make him into an old softie, something that really clashes with DD and Matt. The inconsistencies are more forgivable, sloppy mistakes, such as when Foggy later mentions his proposal to Karen that was turned down, when in fact he never went through with asking her in the first place. Ah well, the meat of what's here is still great, and will go great between Captain America and Defenders Essentials on your shelf.