The race for the seat of retiring Maine GOP Sen. Olympia Snowe has emerged as the perhaps the most critical – and unpredictable – Senate contest in 2012.

Having a crowded field of six Republicans, four Democrats and two independents for the June primary was complicated enough. But former Gov. Angus King — an independent who has yet to say how he will caucus — jumping into the race has even top political analysts guessing about the outcome.

“After 28 years of watching some 950 Senate contests, it has been years since we have encountered anything truly new or even surprising. That is, until this open seat in Maine,” Jennifer Duffy, senior editor for Cook Political Report, writes.