FL-Gov, FL-02. Maybe the single highest-stakes race (in sheer terms of number of constituents, and the possibility of Medicaid expansion for millions of people) was the governor's race in Florida. The race went down to the wire, with Republican incumbent Rick Scott winning by 72,000 votes. The result was a bit of a surprise, since the majority of late polls gave Charlie Crist a lead, albeit a tiny one, usually around one point. The Miami Herald's Marc Caputo's retrospective suggests that it shouldn't have been that much of a surprise; Crist's underperformance in the Democratic primary (where he lost many conservative Panhandle counties to Nan Rich, his little-known opponent) and Alex Sink's underperformance in the FL-13 special election provided notice that they weren't getting their base voters to the polls in the off-year.
Peter Schorsch of St. Petersblog goes into even more detail about what held Crist back. Some things were fixable: Schorsch suggests Crist could have rolled out his campaign later but more emphatically; debated Nan Rich in the primary; or gotten Barack Obama to campaign in person on his behalf. Others issues were more difficult, like getting better turnout from the LGBT community (suspicious of Crist because of his earlier support for an anti-same-sex-marriage amendment while he was still a Republican) and the Cuban community (suspicious of his embargo policies). Weakness with both of those groups can be seen in how greatly Crist underperformed in Miami-Dade County.
Matthew Isbell, on the other hand, thinks that the problem wasn't Miami-Dade but Crist's performance in the aforementioned Panhandle. Crist's weakness in the primary against Rich just continued in the general election: While he still overperformed Barack Obama in most of the Dixiecrat counties, he ran way behind Alex Sink's 2010 gubernatorial performance in those same northern counties, as you can see in the map above. And while Crist overperformed Sink in the I-4 corridor (especially Orange and Osceola Counties), he underperformed Obama in that area.
That contrasts sharply with the results in Florida's 2nd District, one of the Democrats' few bright spots from the election, where Gwen Graham picked off GOP incumbent Steve Southerland in a Republican-leaning district. This is the same Panhandle turf where Crist lagged Sink, but Graham, en route to victory, outperformed even Sink's 2010 numbers. Isbell's argument is that Crist came off as "just another Democrat" here, while Graham's retail politicking skills, as well as residual goodwill voters extended her thanks to her father (the moderate Democratic ex-Senator and ex-Governor, Bob Graham), helped her eke out a victory.