Hear me out and read this whole thing if you can. I agree that ATLA was and will always be better, but some people give this show a hard time. To start, the writers always thought they would only be doing 1 season, then they thought they would be doing a 2nd season. They they got both 3 and 4 seasons put on them by nickelodeon. Now that that is settled:
Legend of Korra has taken place after the industrial revolution in the Avatar universe. YES there will be more lightning benders because it is a skill that will be more widely taught and developed to become easier to generate because it is a skill that is needed for something other than combat. YES there will be more cars and buildings instead of the classic old ATLA dirt roads. YES there will be more metal benders and it will get easier to do as Toph passes on her knowledge (in the comics) and it develops to be much easier. People have to understand that change will happen.
Also, I've seen people who have only watched till the 1st or 2nd season and put in reviews. That's like watching one season of ATLA and saying you hate it because they didn't defeat the fire lord yet. In my opinion, the 3rd and 4th seasons (where the horrible love triangle has finally straightened out) are the best overall, and they fix up most of the "plot holes" people say they have. One person in these reviews said they only watched up to the 1st season and asked how did so many air bison get here, which is explained in the 2nd and 3rd seasons if they would just give it a chance.
I've seen many more bad reviews with other noticeable points to back them up. But personally, I think Legend of Korra is just fine on its own if you give it a chance.
Finally, there is a YouTube channel called "Letts React" and they do a good job on understanding the differences and respect this series for what it is. (This is not my YouTube channel, I just think they should get more recognition) Thank you for reading my rant!