Having played 1/2 my first-GC in EU2, here are my humble thoughts on this topic, listed as EU2's pros and cons.
Pro:
--Better Soundtrack
--More nations to play, or alternatively, more nations to annex

--Expanded diplomacy allows force-vasalizations and gives opportunity for gaining CB on just about anyone if you're patient. Also love the military access option
--Events help guide history to approximate real-life (i.e. Habsburg inheritance of Burgundy, Unification of Prussia, etc.)
Con:
--Army matientience out of sight. I've had to radically demobilize twice to keep competitive in tech races. Also, the AI seems to pay 0 matientence (Cologne's got 42,000 men sitting around, I'm ten times their sizer and would go bankrupt in a month if I kept those kind of forces on all my teritories) (OK, granted the AI needs all the help it can get, but still)
--fortress expansion also hideously expensive
--Event guide history to approximate real life even if the AI nations aren't doing what they need to (i.e. Austria inherited Hungary in 1526 despite the fact that the Ottomans aren't anywhere near Hungary. Thus, Austria gets all of St. Stephen's realm instead of the tiny sliver of "Royal Hungary" that they kept in real-life)
--Stability irritatingly difficult to maintain (i.e. mine falls to 0 through some event, then another event comes along and drops it to -2, I shift my research priorities into stability and get it back up to 0 when another event drops it back to -2, I continue to invest, raising stab. to -1, and another event drops it back to -2, it took the best part of a decade to get back into positive territory)
--2 wars needed to take 2-province countries like Granada and Fez (I'm playing Castile/Spain)
Things I'm not sure of yet:
--Missionaries: love the idea, but they're awfully expensive and they fail half the time
--Domestic Policy: I probably just haven't played enough to get the feel of this tool yet (I keep forgetting to move it every ten years :wacko: )