The Giants have always been traditionally, you know, pretty shitty in the air* but with a solid running game and a killer defense. The team has been shifting its focus over the past few years, though, relying more on the passing game and less and less on the running game and defense to win. Of course, they just had a horrible season last year, so maybe that's not a good thing. ;)
Anyways, it'll be interesting to see where they go with this. It could be really exciting to see this bright young QB come in and transform the team - they've had a pretty decent bunch of receivers now for a while, but with the incredibly streaky Collins behind the line they never knew if the ball would be going to them - perfectly - or if it'd be sailing into the arms of the opposing defense. Hopefully Manning will bring some much-needed consistency and accuracy to the team.
Of course, this poses the question: what happens to Collins? As I understand it he refuses to be the #2 QB, which means they'll have a tough decision: trade him, let him finish out his last year as the #1 and give Manning a chance to warm up, or...? The Giants could really use a solid backup QB, and I think if they were willing, the best of both worlds would be to let Collins finish out his last year as a starter while Manning observed and took the occasional snap, then swap Manning and Collins and let Collins be the best backup they'd have had since... I dunno, Hostetler I suppose.
* - ok, that's not true, but that is the team stereotype. They've actually had a lot of good QBs over the years.