Start with some of the Editor's Choice games and you'll find higher quality for the most part. An example might be games by Snowman (Skate City and Where Cards Fall, and Alto's Adventure and Odyssey non-Arcade). I don't currently subscribe to Arcade, and am waiting for The Pathless from Giant Squid (who created Abzu), which should be coming soon. Generally the games I like best on iPadOS are those published by Annapurna Interactive, but I don't believe any of them are in Arcade.
Edit: hmm, now I'm not sure there is an Editor's Choice category in Arcade, or at least it's not showing today. Maybe that's only in the full store.
Touch Arcade is a good source for mobile game reviews. It's also at the bottom of the MacRumors home page.