LJ summed it up best as usual! BB1 is legitimately one of the funniest seasons of reality TV ever from start to finish and it's the perfect introductory piece to BBCan. Do *NOT* get spoiled whatever you do because the funale is a legitimately surreal experience.
BB2 is also very good and The People's favorite season. The start is a bit slow, but holistically it has the best and most satisfying narrative. A very good season, but the reason I don't like it as much as BB1 is because I didn't care AS much about the characters. There were definitely people to root for in BB2, but I loved my favorites from BB1 more and hated my least favorites from BB1 more.
BB3 is just okay. The opening weeks are atrocious (I feel like by this point it's commonplace to not judge a season until the rigging starts), but the season still ended up being alright. I don't understand the claims about how this season had the best gameplay because there were so many twists and so much rigging that it didn't even resemble a game of Big Brother

easily the weakest of the three, but it's still much better than most of the recent BBUS seasons alol.
BB4 is also firmly just okay. I'm not sure if it has to do with the move to Global or if the show has just gotten stale after the first two seasons, but there is a huuuuge gap in quality between BB1/2 & BB3/4. Again, the opening weeks haven't been too stellar and the cast is very vanilla and bland. The jury is still out since we're only like 35% through the season.