I got round to watching this episode again last night and I enjoyed it more than when I first saw it.

On reflection, it is not weighted with the "little" clues that Columbo and the viewers find fascinating, but it does feature excellent interplay between Falk and Clive Revill, as the charasmatic Joe Devlin. The episode almost reminds me of "Any Old Port in a Storm" in that it mirrors the increasingly harmonious relationship betwen Columbo and Adrian Carsini. Although I'm surprised that Columbo wasn't more aggressive when he found out what Devlin was really up to!

In fact, Revill's characterisation is brilliant. He is outwardly a typically jovial, fun-loving, joke-cracking Irish man, but inwardly he carries a harmful, vindictive streak which stems back to his days as an Irish terrorist. This is borne out when he smugly rolls the whisky bottle along the floor with his foot, after committing his murder, so that it is right next to his victim...

Columbo's pre-occupation with the whisky bottle is the over-riding clue of this episode and the scenes in the Irish pubs have a certain charm about them (I still don't know how Columbo managed to beat Devlin at darts, when he needed 66 and threw it with one dart!).

Well-worth watching: I always wondered at the end when Columbo scratches the whisky bottle and replicates what Devlin has been saying throughout the episode "this far...and no farther"; whether it was a thinly-veiled reference to Falk hanging up his mac as Columbo, as this was the last epiosde in the original series?

Agreed, this episode was a fine way to wrap up the series, and yes "this far and not farther" is said by Columbo to indicate this. Although in many of the later episodes, Columbo becomes more arrogant and goofy, in this episode he returns to form as the humble, but intelligent sleuth.
Clive Reville was absolutely superb. I can watch the scene where he is telling the story about his arrest at the fundraising gathering over and over. Even though there are a lot of filler scenes (the limericks, the radio show, etc), they are add to the story. I particularly love the limerick that states (approximately)

There once was a man named Finnegan
who broke out of jail to sin again
He broke laws by the dozen
even stole from his cousin
so the jail he broke out of he's in again

(see, I love it so much I memorized it!)
Of course, Finnegan is really Joe Devlin himself who stole from the Irish-Americans who donated money to help the victims but he used to buy weapons.