Militarily, hardly at all. The Visigothic army was built out of a core of predominantly Gothic soldiers who had fought as part of the Roman army, along with other defectors. They had Roman weapons, Roman armour, Roman tactics etc. As of 410, if you put a Gothic and Roman soldier next to each other, they would look very similar and would fight very similarly.

Their leader, Alaric, had held many military offices in both the western and eastern halves of the Roman army. In 397 he was appointed magister militum per Illyricum, and appears to have been promoted to magister utriusque militiae in 399. Alaric was an excellent commander, well respected by Roman administrators. When Alaric made the decision to march on Rome, he had previously been preparing to march under the Roman banner to re-secure the Balkans for the Western Roman Empire.

From what our sources (Claudian the poet, Zosimus, Jordanes, occasional references in other histories) tell us, Alaric was not alone in this. Goths, for some unknown reason, crop up frequently in positions of command across the sources. In 399, the Goth Tribigild rebelled for unknown reasons, but he clearly commanded significant influence as he called for the dismissal of Eutropius, a hugely influential figure in the Eastern Roman Empire. From 398-9 the eastern field army was commanded by the Goth Gainas, who was sent to negotiate with Tribigild but ended up joining him. When the position of magisterium utriusque militiae became available in the western half of the empire there were two Goths considered for the position: Alaric and Sarus. When we think of Goths and barbarians more generally we often picture a disorganised and ill-disciplined horde, but the Goths could comfortably command armies just as well as a 'native' Roman general in the Roman style. The 410s were arguably the peak of Visigothic military capability.

In the field, there would not have been much difference between the technology of the armies. The one thing the Goths could not produce which the Romans could was artillery, but the Roman use of artillery was in rapid decline anyway and Ammianus Marcellinus - who loved artillery and mentioned it frequently - makes almost no mention of it after Julian's disastrous campaign against the Persians in 363.

What the Goths lacked was naval technology. The Visigoths, for some reason, simply did not build ships on any notable scale. The Romans had a small navy to patrol trade routes, which could be called up to build a more substantial navy. This wasn't much, but it was better than anything the Goths could put together.