You can play it without mods but I feel you will get more out of the game if you install some, a lot of them are QoL type things.
I'm falling so far behind my friends because I just don't have the time to play. They're 880+ with multiple legendaries across their toons (both have 2 on their mains) and I'm still stuck at 868 with 1 bad legendary. I'm loving the game but I can't keep up with them and am having to play a lot on my own.
I know that's the nature of MMOs, the more you play the more you get out of it.