THE appeal of tonight's clash of Munster and Leinster at Thomond Park (6.45) is greatly enhanced by the level of the unknown that accompanies the fixture after a close season of remarkable change.
Departures, retirements and the rigours of a Lions tour have meant that team-building plans have been fragmented to say the least.
Tonight's encounter is the fifth game of the competitive season for both sides, but is also the first true test. With due respect to their opponents so far this season, it is only when these rivals are pitched against each other that we get a true sense of their well-being.
They invariably bring out the best in each other. It's not always pretty, but it's full-blooded. Ireland assistant coach Les Kiss' confirmation during the week that, in a throwback to years gone by, this game is an unofficial "Ireland trial," makes it all the more exciting.
Leinster go into the game with the more settled side as their selections have been more predictable and they have absorbed their returning internationals and Lions in a more balanced manner.
Munster, in contrast, have gone into each of the four games in experimental mode, as if Rob Penney was dipping into a bag of liquorice allsorts, mixing and matching as he drew his selections forth.
Munster are again in such a mood at Thomond. How else could you describe it when players like James Coughlan, Paul O'Connell, Casey Laulala, Keith Earls and Felix Jones will be playing together for the first time this season?
The absence of Brian O'Driscoll with a calf strain is a blow to Leinster. He is also rated as doubtful for their opening Heineken Cup game and Matt O'Connor is giving Lote Tuqiri and Gordon D'Arcy a test run-out together in case O'Driscoll doesn't recover in time for next weekend's assignment.
The biggest issue for both coaches is the choice at out-half. Munster's JJ Hanrahan showed his potential against the Dragons last week, but Penney has reverted to his confirmed first choice in Ian Keatley for tonight.
Leinster boss O'Connor has been generous in his praise of new signing Jimmy Gopperth, but Ireland head coach Joe Schmidt will be relieved he has opted for Ian Madigan this weekend. Schmidt, of course, will hope the 24-year-old Blackrock graduate will see regular action at No 10, with the chance to back up Jonathan Sexton up for grabs.
That Keatley has been overlooked for the November internationals must rankle, given he has been the most impressive of the Irish No 10s so far this season. The face-off between him and Madigan is another of the fascinating storylines in this game.
The rivalry between Leinster and Munster has enriched Ireland's rugby history and yielded a ready supply of talented players for the national team.
First it was Munster and their incredible work ethic which led to a double success in the Heineken Cup. It marked a period of dominance over their Leinster rivals.
Leinster's emergence from that period of playing second fiddle to Munster was processed on a more extravagant game plan that perfectly suited the collection of talents on their roster.
They are now the standard and Munster are scrambling to catch up.
This provides another intriguing background to a game that will serve both as an important benchmark for the two sides and as a significant exercise for Schmidt and his management team as they assess their options ahead of the November internationals.
Unsurprisingly, Schmidt is leaning heavily on his old club, with 20 of the Leinster squad being backed up by the co-opting of Richie Murphy and, most likely, Greg Feek from the Blues coaching staff for the games against Samoa, Australia and New Zealand.
Seventeen of those Leinster players are involved tonight – either starting or on the bench. When combined with the 11 Munster players in the Irish squad, Schmidt and his coaching staff will be able to assess 28 of those who will feature in November.
Munster, with three wins from four, are a little more advanced in their seasonal development, but it has yet to be determined if their more influential players have bought into the more expansive game envisaged by Penney or if they believe they are better served by reverting to the style of play that provided them with the outstanding highlight of last season – the win over Harlequins.
Last season slipped by without the team showing the ability to process a more open game behind the scrum and any consistency and improvement in this area this season has been marginal.
However, at least they have curbed the tendency to keep passing the ball flat along the line until it ended up in touch as it did so often last season.
They showed against Dragons last weekend that they lack penetration and a player or two to hit the line at an angle to wrong-foot the defence. They failed to play with any real coherence.
Significantly, their only two tries came from forwards – James Cronin and Peter O'Mahony – driving over in the traditional Munster fashion.
Events so far suggest O'Connor has a clearer picture of his best 15. Yet it is possible for those about to return for Munster that they will slot in seamlessly. O'Connell, after his substitute appearance against the Dragons, Coughlan, Donnacha Ryan and Keith Earls are all experienced pros who will not take long to get up to speed.
At their best in recent seasons, Leinster were the style masters of Irish rugby, Munster the efficient, but less flamboyant artisans.
At this stage of the new campaign, though, neither has settled fully into the weekly routine. It is, thus, too early in the season to expect a match to compare with the many spectacular contests these teams have given us over the years.
But you can bet it will be as intense and as competitively fought as ever with these two great rivals seeking to establish early-season bragging rights.
MUNSTER – F Jones; K Earls, C Laulala, J Downey, S Zebo; I Keatley, D Williams; D Kilycoyne, M Sherry, S Archer; D Ryan, P O'Connell; P O'Mahony, N Ronan, J Coughlan. Reps: D Varley, J Cronin, BJ Botha, D O'Callaghan, CJ Stander, C Murray, JJ Hanrahan, D Hurley.
LEINSTER – R Kearney; F McFadden, L Tuqiri, G D'Arcy, D Kearney; I Madigan, E Reddan; C Healy, S Cronin, M Ross; M McCarthy, D Toner; K McLaughlin, S O'Brien, J Heaslip. Reps: A Dundon, J McGrath, M Moore, R Ruddock, D Ryan, I Boss, J Gopperth, L Fitzgerald.
REF – R Poite (FFR).
Munster v Leinster
Live, RTE2, 6.45