The tournament commenced with England being beaten by France, who were trounced by Wales, who had previously been played off the park by Ireland, and all four countries still have a chance of finishing at the top of the heap. There will not be any grand slams, but then, considering the importance of home advantage, one always doubted whether any of the participants had the all-round strength to win five matches in a couple of months.
The odds still favour the Irish, who tackle the Italians next in Dublin, but their frustration after being edged out at Twickenham on Saturday was wholly understandable. On another day, with a more eagle-eyed referee, England might have lost personnel to the sin bin or conceded penalties during their defensive effort at the denouement. Yet the eventual 13-10 victors are a team on the rise and, considering the youthful nature of Stuart Lancaster's squad, one can anticipate them growing in stature as the 2015 World Cup draws closer.
By comparison, Ireland have the look of a rock band on a farewell tour and, for all that Brian O'Driscoll has been one of the genuine greats, there was plenty of huffing and puffing from the 35-year-old, but precious little inspiration about his performance in London. The clock has caught up with him, as it is doing with the talismanic Paul O'Connell and Mike Ross, and that triumvirate's imminent departure will leave a huge void.
They will expect to prevail over the Azzuri and have every chance of defeating France, which would hand them the title. But there will still be mixed emotions among their supporters, as O'Driscoll strides off the Test stage for the last time next month. Irreplaceable? Of course not. But a hard act to follow? Unquestionably.
Wales, for their part, have experienced the sort of wildly fluctuating fortunes which help explain sport's appeal. While they were being dismantled by the Irish, their display featured so many botch-ups, basic mistakes and brazen blunders from their Lions fraternity that one feared Jonathan Davies might spontaneously combust in the commentary box.
But, to their credit, the Welsh heeded the warning from their coach, Warren Gatland, and were far too potent for the French on Friday. Wherever you glanced, from the marauding power of George North and Jamie Roberts, to the revitalised Gethin Jenkins and Adam Jones, and the back-row trio, Dan Lydiate, Sam Warburton and Taulupe Faletau, this was an ensemble bursting with talent. And yet, when any XV goes from losing by 23 points to winning by 21 in the space of a fortnight, one wonders how they will fare the next time against England.
That match on March 9 promises to be a classic, especially given the history and hostility between these nations. But England have gathered real momentum and their pack will provide greater problems than the anaemic French.
As for the latter, Les Bleus continue to veer between mesmerising moments and misfiring mediocrity and Philippe Saint-Andre seems no closer to finding the right balance between glamour and grit than when he arrived in the job. If his charges are as feckless on their travels again, Scotland may fancy their prospects at Murrayfield. But if they can reproduce their opening 40 minutes from the match with England or the try-studded 10-minute spell which floored Italy, anything is possible.
The "Big Four" all have a Jekyll-and-Hyde quality to them. It is just unfortunate that with the other two national sides, you know exactly what to expect.