I have a little bias towards tacticall and non-floaty FPS, if you have the same taste, then you will absolutly love this game.
To give a little background, my previous favorite FPS were old Battlefield games (BF2, BF2142 and Bad Company series), liking a lot the mechanics from games like Killzone. I liked the premise from Counter Strike game but I did not liked the floaty feel when holding runing and shooting a gun.
When Rainbow Six Siege was released, I was a bit thrown off because I got the impression that it was going to be a lot like counter strike's mechanics, I got into the game on year 2, after a friend convinced me to try it, and it completely changed my perception of the game.
Siege is a tactical shooter, with robust NON-FLOATY gun mechanics and MOBA souce on top, it is the evolution of the genre with a lot of care into the community and balancing.
You always learn on every single round and match, I have over 500 hours, and I am still learning new things from other players, the games is very rewarding with deep mastering learning curve.
It has grown on my and has become my favorite FPS of all time, and it is in my top 10 games of all time for sure.