You can't listen to others' opinions. You have to give the job some time. Some people love working at Wal-Mart, some like it, and some hate it. I worked there almost 30 years ago. I had a fanatic store manager that worshipped the Wal-Mart god. While he was there, I hated my job. He was transferred to another store and I was moved from the men's and boy's department to the register. That was just okay. I had taken the USPS exam, made a very good score on it, and was offered a job with them. I worked 2 jobs during my 90-day probationary period with the USPS and resigned from Wally World once the probation was over.
I have said I will never work at a Wal-Mart again. I may work for my local Sam's after I retire from the USPS.
It is not the greatest company in the world to work for but as you stated a job is a job. There are advancement opportunities. Go in with the positive frame of mind, ignore the complaining and do the best that you can do. You might find that you really do enjoy it. Congratulations on your new job.
Everything you said about Walmart can be said about any retail job. If you don't care for these things then you should look for work in another industry.
Dont get yourself down about it even before you begin. Going into any job with a positive attitude can work wonders in your favor.