The lead changed hands five times at the Aviva Stadium, with Ireland appearing to have won it through a Tommy Bowe try before George North hit back with Wales' third score to set up Halfpenny's heroics.
The match has got the new 6 Nations campaign off to a cracking start but Guscott says it doesn't quite top his list of most impressive matches in recent seasons.
Guscott, who toured three times with the Lions in the 1980s and '90s, believes the second Test between the Lions and Springboks in 2009 is the hardest-fought encounter he has ever witnessed.
Britain and Ireland's elite were beaten 28-25 by the then World Champions in an absolute thriller in Pretoria as the Boks clinched an unassailable 2-0 series lead.
The Lions led 10-0 inside the opening 10 minutes and 16-8 at the break but the Boks hit back to win it at the death with a last-minute penalty from Morne Styen. The replacement fly-half hit the target from halfway after Ronan O'Gara made contact with Fourie du Preez in the air.
Throw in four outstanding tries, Schalk Burger's first-minute eye gouging of Luke Fitzgerald and a truly incredible atmosphere at Loftus Versfeld and it's no surprise that Guscott finds it hard to find a better Test match than this one.
"Ireland v Wales was a pleasure to watch and must have been a rollercoaster to play in - what a fantastic promotion of the great game," Guscott said in his question and answer column on the BBC Sport website.
"The hardest fought game I've seen in recent times was the second Test on the Lions tour in 2009.
"The physicality of that match was so intense you could have got winded just watching it."