Fridge Brilliance: Each Spidey having a different voice actor - Ultimate's a teenager, Noir needed to sound grittier, and 2099 isn't even Peter Parker.
The order of the Spider-Men on the cover is by alphabetical order by dimension. 2099, Amazing, Noir, Ultimate.
The fact that Amazing Spidey could defeat the Juggernaut in a fist fight seems impossible until it's revealed that when activated, the Tablet interferes with the power of the Crimson Gem of Cyttorak, so it may be safe to assume that it's been doing it the whole time, even when it wasn't activated.
I just figured the bar wasn't showing Juggernaut's health, but how much more of Spidey he would tolerate before trowing him. And in the close-quarters part, Spidey wasn't holding back (since it's the Juggernaut) and he was just moving to fast for Juggernaut to react.
Under Mood Whiplash, it's noted that Ultimate Spidey continuing to make one liners during the Carnage level felt out of place considering what's going on around him. But think about it - He's still making one liners so that he keeps his head & doesn't freak out from Carnage killing everyone.
He realizes in his first fight with Green Goblin in the comics.
Fridge Horror: If Noir dies from Vulture biting him in the punch-out segment, it's likely that it's because his face has been bitten off.
If you take Carnage's stage into consideration, if Ultimate Spidey failed, the damage would likely have been long term and nearly impossible to fix, if it would even be fixable in the first place, and even then, the end credits become a lot less comforting and humorous when you think about this more and more, because it confirms that there are still a few zombies left.
Fridge Horror: Judging by Deadpool's comments about Spider-Woman, Ultimate Spider-Man's segments are set after the Clone Saga, meaning that you've left Gwen Stacy trapped under burning rubble.