It's a difficult subject since we have few direct and mostly derived sources explaining Dacian language. The few that claim to be direct were mostly Romanian forgeries under Ceausescu that contained blatant anachronisms. I forget the name, but there was one tablet or something that was supposedly a Dacian message during the Roman wars and it mentioned Christian derived names like Maria that could not have been used in Dacia at the time, and it was also written in an obvious creole that contained modern Romanian Latinisms as well as other elements.
However, whatever we do have shows that it was a Satem language and somewhere actually very close to the Balto-Slavic spectrum. Also interestingly, it shared some elements common in Albanians and Romanians, as well as some other Romanian influenced or derived populations.
Geographically they spread out much farther than just Romania. The Getae themselves have been present on the southern Danubian plain, and may have extended into Bulgaria as well prior to the Celtic invasions of the 3rd century BC under Brennus (no, not the one who sacked Rome), who ruined their capital of Helis, which may have been near Sveshtari. Other Dacian tribes have been present in Ukraine and Moldova, namely the Carpi. Under Burebista there was also further expansion that led them to create loose communities farther out. Supposedly they even west as far west as the Noricum region of Slovenia. In the northern expanse, a tribe related to the Carpi seems to have created Setidava/Getidava as far north as Znin in Poland (the exact location is disputed), forming a new tribe of Costoboci.
In general the Carpathian region seems to have been a strong domain for R1a and R1b migrations, and from my understanding of the early Indo-European migration patterns and the "Scythian" ethnographic qualities of the Dacians and in particular the Getae, they would at least have been as northern plotting as modern Slavs, if not Balts. Militarily they seem to have focused on more hit-and-run and ambush tactics, including the use of poisoned arrows as the later encroaching Slavs were reputed to do. Procopius even considered the Sklaveni as synonymous with the Getae.
As far as looks go, the busts and other shows of appearance make them look a very Yamnaya or Bell-Beaker long skulled but still broad and brachycephalic type.
https://encrypted-tbn0.gstatic.com/...dJxK2Kp8PaxOAqTyeLrut-lXYIrmv6SeSQQNe7UA1TgOt
https://statuidedaci.ro/images/statui/roma/muzeulcapitolin/statuie-dac/cap1.jpg
https://upload.wikimedia.org/wikipedia/commons/8/8a/Dacians_people.JPG
Maximinus Thrax, who judging by the geopolitical playing field of his time, was likely rather Getae than "Goth", along with Alanic. He reminds me of Mariusz Pudzianowski:
https://upload.wikimedia.org/wikipe...px-Maximinus_Thrax_Musei_Capitolini_MC473.jpg
So at the least, if they weren't Slavs or vice-versa, there was at the very least a close level of ethnographic kinship.
Modern Romanians do show a notable southern influence genetically, so there's that to show for a migration from the Balkans.