I must be the exact opposite of you guys - I finish very few games compared to what I buy. However, it's mroe because I keep thinking I'll have time in a week or two, and so far I never have ;-)
Case in point - I have (no kidding) probably about 50 X-Box games, including most of the big guns (Halo, KOTOR, Ninja Gaiden, etc.), and yet I've finished probably only 10 out of the 50. I still keep getting new ones, though - I just got Prince of Persia and Dynasty Warriors 4 this weekend, and I'm still working on Medal of Honor - Frontline, Buffy 2 (not as good as Buffy 1, IMO), and Halo.
I need a good month or so of hard-core gaming just to narrow it down from 40 unplayed to 20 unplayed. Maybe over the summer, after my current research project is done....
Also, my wife steals the damned thing - the last three weeks, she's been playing True Crime and Medal of Honor (and beaten both), and God only knows what she'll start next ;-)
Holy crap - I just realized while typing this - my wife has actually finished more X-Box games than me :-O