Offensively, the team was one of the worst in the league. Their 613 runs scored beat out only the Mariners in the AL (plus the Pirates and Astros in the NL), and their .309 wOBA^ was just a hair ahead of the Angels' for 12th in the AL. A wOBA that low should still have translated into around 645 runs (also terrible, but not quite as terrible), but the O's had below average baserunning (if only by about 5 runs according to Baseball Prospectus) and grounded into 154 double plays (the third most in the majors). A .259/.316/.386 batting line will just not get it done in the AL East, and the offense showed neither the ability to get on base (their 6.9% walk rate was just a tiny fraction of a percent better than the Astros', who had the worst mark in the majors - and the next closest team was the Royals at 7.6%) or to hit for much power (their .127 ISO^ was 7th worst in the majors, with only four teams finishing with fewer extra-base hits than the Birds; the M's, A's, and Padres (all in pitcher's parks), and the Astros). According to FanGraphs' plate discipline stats, only the Giants swung at pitches out of the strike-zone more than the Orioles did. The three O's who had the lowest chase percentages? Nolan Reimold, Garrett Atkins, and Craig Tatum. Only Nick Markakis, Ty Wigginton, and Luke Scott were better than average amongst those with at least 300 PA, while Adam Jones, Cesar Izturis, Corey Patterson, and Felix Pie were all amongst the worst in the majors. One masher in the middle of this line-up just isn't going to be enough. The team got just a .280 wOBA out of their first-basemen in 2010, but even replacing them with Albert Pujols would have left the O's barely above average and still pretty firmly with the worst offense in the AL East. They need progress from virtually every player, a delay in the aging process from some veterans, and a bat or two from outside the organization.
The pitching was also terrible. A 4.59 ERA seems decent, but with the lower run-scoring environment this year it was still the 4th worst in the majors. On top of that, their 4.57 FIP^ was 2nd worst and their 4.62 xFIP^ was dead last. The relief crew was solid (4.44 ERA, but 4.25 FIP and 4.15 xFIP), but the starting pitching was pretty atrocious (4.67 ERA, 4.74 FIP, and a 4.87 xFIP that was easily the worst in the majors). The rotation didn't strike out any batters (5.6 K/9), walked a fair number (3.2 BB/9), and gave up some longballs (1.2 HR/9). They were one of the most extreme flyball staffs in baseball, which isn't going to play well in a place like Camden Yards anyway. Combine that with more balls in play and extra baserunners, and it's pretty obvious why the starting pitching struggled most of the season.
Defensively, the O's graded out as one of the worst teams in the majors for most of the season according to UZR^, though things turned around some later in the year and they finished only 23rd at -25 runs. Plus/minus had them at -5 runs (but the league average was around +10) - with +5 of those runs coming from the catcher (via steals), which UZR doesn't account for. If you wanted to say they were anywhere from -10 to -30 that would seem pretty reasonable to me, but that still points to some less than stellar glovework. In fact, things look worse when you take out the outfielders throwing arms (which were rated as saving 8.2 and 20 runs by UZR and +/-).
Bad hitting, bad pitching, and bad defense is going to give you a bad team, and that's what the 2010 Orioles were. Their 66-96 record was actually better than their Pythagorean record using actual runs scored and allowed (63-99) or their record using wOBA, xFIP, and the defensive stats to get expected runs scored and allowed (also 63-99). I'd be lying if I said I wasn't disappointed at the way things turned out.