I had been at one point just prior to the pandemic balls deep in MTG, both cards and Arena, but havent played since.
Ive heard mixed reviews on it lately in that it can get very costly.;
I've been playing it for free since Beta. Sure, investing money would help me get certain cards faster, but I don't feel like not investing $$$ is hurting me. Overall, I like it. It's got good gameplay. I use it to familiarize myself with the new sets/cards/strategies/decks before investing money IRL.
The unfortunately problem is that Arena has been releasing "Alchemy"sets, which are digital-only cards. There aren't enough game formats that are "Paper-only" formats. There's Standard & Explorer. That's it. I like to play "Brawl" (formerly called "Historic Brawl"), which is 100-card Singleton with a Commander. I prefer that format because my real-life playgroup really only plays Commander anymore.