The primary race ended pretty much as the punditry though it would with a landslide win for Martha Coakley. She had multiple advantages over her rivals...advantages good for any person seeking office.
Name recognition - critical in any race, especially a short race where her opponents simply could not distinguish themselves.
Money - she was well funded and drew a lot of money from left-leaning liberal groups (Emily's List) across the nation.
A committed organization - having run statewide in the past, Coakley had an apparatus in place whilst her opponents had to build them in many cases from scratch.
The Sisterhood - being a woman running against three men certainly distinguished her further and helped her in terms of the voters who vote in Massachusetts Democratic primaries.
Additionally, Coakley benefited from being on message, making very few mistakes, and being able to remain above the fray as her opponents fired shots at each other. It is very hard for an opponent to pick on a female candidate (Rick Lazio vs. Hillary Clinton in the 2000 NY Senate race comes to mind).
A few thoughts on her vanquished opponents...
Capuano - played the tough city kid a bit too much and potentially turned off certain voters. He played Mr. Insider who brings home the bacon - this plays well in certain areas, but also reinforces perceptions of the "old boy network" Capuano has a lifetime US Rep seat (although he did really underperformed in his own district).
Khazie - ran as the idealistic reforming outsider and nudged Pagliuca into last place in the process. He did surprisingly well in the wealthy liberal areas in the immediate Boston suburbs and I think may have laid the groundwork for a future run, perhaps for a statewide office as there may be a number of open seats this upcoming November.
Pagliuca - someone has calculated that he spent about $150 per vote in his last place finish. Classic story that money does not always buy happiness - or a Senate seat. He was hurt by past support for Mitt Romney which did not endear him to liberal primary voters. Additionally, he took many liberal positions that seemed it bit like "me-tooism".
Wonder if Steven Lynch is regretting his decision not to run. As the only conservative Democrat in this race he may have made it more interesting...
Bottom line is that Coakley's advantages were going to be hard to overcome by anyone in this type of primary. She racked up large victories in the voter-rich suburbs around Boston and in Western Massachusetts. If it had been a two-way race between her and Capuano, it may have been closer as there would have been a different dynamic in place.
Onwards to the final election!