Couple of things. Some are quite close to facts in my mind, some are speculations about how i perceive the game, so kindly correct me if i am wrong. I don't see myself switching but hey, who knows.
Flow is the first one that comes to mind. A bit of what groundhog wrote. It is more dynamic. I also prefer the strength/speed/endurance/technique balance that rugby brings to the table. Athletes in rugby are undoubtedly worse "specialists" but, on average, appear to be better rounded (the fastest footie player will be faster than the fastest rugby player, but the slowest rugby player will be much faster than the slowest american football player. Same with other skills).
In rugby all the players have to be reasonably good at the basics (running, tackling & passing). If they are not, chances are their team will pay dearly for that sooner or later. Some of the US 7s rugby team came to mind while i was typing. It's not just about becoming exceptional at one thing, but also about not being terrible at the rest. The word "balance" comes to mind.
The next one is more my perception, so please correct me if i am wrong, but i have a feeling that there considerably more room for improvisation in rugby. You can plan a 30 sec sequence of event rather accurately i suppose. Can't even fathom the idea of estimating the possibilities within 5 minutes of straight rugby. (this one kinda ties in nicely with the previous one; harder to improvise when everyone is a specialist). I like a bit of both (planning vs improv), and rugby appears to have that.
And last, time. Am football appears to take so bloody long.
Time zones don't help (me) either.