go back and reshoot a ton of scenes, especially the ending.
I distinctly remember the trailer being very cringeworthy. The "I rebel" quote came across as almost meme-worthy funny and I had no desire seeing it.
Yet, I went anyway and it is by far the best of the modern Star Wars entries. If you add TV shows, Mandalorian 1st Season probably edges it out for the top spot, but it's close.
I also feel Solo is underrated and works for me with multiple viewings. It suffered from the Last Jedi being such a horrendous movie, I believe it would have been rated much higher had it come off the heels of Force Awakens instead.