I started off with tretinoin a few years ago but gave it up after a year. I found it a bit harsh and didn't enjoy how careful I had to be about using other products with it. I now just use other retinoids including Medik8. I also rate Sunday Riley A+ and Paula's Choice 1%.
I also really like the Augustinus Bader one but can't honestly recommend it (outside of getting the odd one in advent calendars) due to the daft price.
I guess most people build up from normal retinoids to tretinoin but I did it the other way around. I feel like that year of using it did kick start my skin being better and I seem to be able to use most strengths of off the shelf retinoids with no issue - perhaps due to that initial course of tret.
I haven't noticed any downsides of stopping. My skin has continued to be in decent shape. Maybe I'd look better long term if I'd kept using it but I found it to be a bit limiting and didn't like using a subscription service.