Wincing at an off-beam impersonation of Neil Diamond by his colleague Steve Coogan, Rob Brydon quickly ad-libs an explanation: "Martin Sheen sings the songs of Neil Diamond, out now..." In response, Coogan later wonders if Brydon has done so many adverts that he now thinks in voiceovers. That's The Trip to Greece, which begins with Coogan dismissing the entire Welsh oral tradition ("in Manchester, we can read and write") and gets pricklier and funnier from there. Watching the last series, The Trip to Spain, I felt like this show could continue for as long as Coogan and Brydon have new career landmarks to jab at each other over. The stars and director Michael Winterbottom, perhaps wisely, have decided not to push it. This is reportedly the last Trip, although you can never bet against comebacks nowadays.

There is a lot of banter about getting old here, but for a while that just feels like part of the comedy. It's increasingly hard to miss, as a lot of people have observed, that Coogan and Brydon's stable of impersonations are rooted in their 1970s boyhood: Michael Parkinson, Roger Moore, Ronnie Corbett. There are some new ones here - the bulk of one episode is devoted to them re-enacting Marathon Man, passing the Olivier and Hoffman roles between each other. Coogan also takes a brief but very much appreciated stab at Werner Herzog. Elsewhere, the mimicry reaches bizarre conceptual heights, with Coogan impersonating a stop-motion monster and a badly-dubbed actor, a cherishable impersonation of Ray Winstone playing Henry VIII, and Brydon doing a one-man rendition of Vangelis's score for Chariots of Fire.

The Trip to Spain is perhaps my favourite of all the series, largely because it's the one where Winterbottom seemed most content to rest on the duo's natural dynamics. The earlier series had constructed professional and personal crises for them to navigate, which never quite suited Brydon. In interviews, Brydon has said he'd quite like to do more straight acting and film roles, but not if it takes him away from his family. It's that satisfied quality, the failure to be consumed by professional setbacks, that makes him so funny opposite the restless, ambitious Coogan. The Trip gave him an extramarital temptation and The Trip to Italy gave him a big movie role, but Brydon is funniest when his contentment is driving his co-star mad.

There is a gratifying amount of that here. In preparation for their Greek odyssey, Coogan has read Homer and Epicurus, and talks about Byron swimming the Hellespont. Brydon hasn't and doesn't care. About four out of six episodes are fuelled solely by this dynamic, and it never gets old. Even I, a binge-watch skeptic, wolfed down the entire season in one sitting and could have gone for more. Episodes four and six try something different, trying to bend the series to some kind of close, and those have settled less well with me.

As we watched, my friend Oliver jokingly wondered if the finale was going to involve Coogan snapping and murdering Brydon, but that's not it. Episode four brings two female guests in to share their lunch, which is presumably meant to bring some macho competitiveness out of the pair. Given that there are several episodes of The Trip that consist mainly of them fighting over who can impersonate Michael Caine better, I'm not sure they need the encouragement. The result doesn't add to the show, but it doesn't detract. The final episode is more of a problem, folding in the real-life death of Coogan's father. It's a risky venture, but The Trip has flirted with melancholy before, most notably in the downbeat ending of the first season.

The last episode of The Trip to Greece clearly means a lot to Coogan, but Winterbottom seems strangely unsure how to handle it, slathering on the maudlin music in an objectionably heavy-handed way. It's also strange that, if this is Winterbottom's final statement on Coogan and Brydon's relationship, we don't see this brush with mortality affect that pairing. The news of Coogan's father's death happens right as they go their separate ways. There is a lot of cross-cutting to play up their contrasting home lives, but we never learn what this friendship looks like when tragedy strikes.

I realise I'm in danger of becoming a stuck record here, but I do wonder if the sheer flabbiness of modern television, the acceptance that there'll always be an extra season or five to tidy up loose ends, has led to a lack of focus on dramatic unity. The recent season finale of Doctor Who paid off ten episodes of the companions wondering if they really knew the Doctor with huge revelations about her past... delivered while the companions weren't around to hear them. Oh well, there's always the Christmas special! But there may never be another Trip, and this one is stronger on business as usual than drawing things towards closure. That said, after noting the earlier seasons struggled to dramatise Brydon's personal life, I was delighted to see him greet his wife in the final episode with a barrage of impersonations. That idea - that the real Rob Brydon is exactly the same man who's been slowly driving Steve Coogan mad - felt more organic and insightful than any of the more dramatic material.