I haven't seen many of the other DC movies – so my opinion comes with a grain of salt of not being a longtime fan. With that said, I felt like I didn't need any extra knowledge at all.
The movie was surprisingly good, from multiple angles. As an R-rated action film, things never slowed down. Despite its runtime, the movie goes at a whip-smart pace, with many set-pieces, moments of surprising tension and conflict, not to mention inventive deaths just when you think you've seen it all. As a comedy, the movie has a number of funny one-liners, comic twists, and a great group dynamic. And from a dramatic standpoint, there is surprising depth to many of the characters on screen. When you get attached to unique characters such as King Shark, Polka Dot Man, and a rat named Sebastian (as well as the more complex, traditional leads, of course) you know the movie has made the most of its characters. Many of the deaths throughout the movie cut, even with a promotional tagline of "Don't Get Attached" and a cast list a mile long. The movie also manages to have multiple touching and thought-provoking themes, motifs, and character relationships amidst the R-rated humor and gore.
All in all, the production was wonderful. The cast did a bang-up job – Robbie, Davis and Elba are obvious, but Kinnaman, Cena, Melchior, Capaldi and Dastmalchian too; James Gunn was fantastic as usual; and cinematics, styling, and color were on point. I assume that this movie has redeemed, or at least built upon, its predecessor. Go see it if you want a good time.