Agricola marched further north than any other Roman leader, but this doesn't necessarily make him the most successful. I'd argue that Aulus Plautius, in conquering the rich and populous tribes of the south, made much greater gains for Rome. Caledonia, especially north of the Forth, had very little economic value. Agricola's forts were soon abandoned and by the end of the first century the Romans had completely retreated from what is now Scotland. The Romans twice invaded Caledonia again, and both times they eventually gave up the territory they had gained. From Dio Cassius's account of the Severan campaign, you really get an impression of how hard it was to lock down territory in northern Britain.

We should bear in mind that Agricola's biography was written by his son in law, Tacitus, but he nonetheless comes across as a particularly able commander. His advance into Caledonia was cautious and supported by a supply fleet. Tacitus describes two battles that Agricola fought in Caledonia. The first was when the camp of the Ninth Legion (ever unlucky in Britannia) was attacked at night, and Agricola dispatched reinforcements. The second was the great clash that occurred at Mons Graupius. I'll add a link to an online text of Tacitus's Agricola, so you can read about the battles yourself. Remember that classical historians are not always reliable; Calgacus's speech is almost certainly completely of Tacitus's own composition, and it's possible that the Caledonian army and its casualties were much lower than claimed. https://sourcebooks.fordham.edu/ancient/tacitus-agricola.asp