I own them all on BD, most in more than one edition. Tarkovsky is one of my favourite filmmakers. He never made anything that was trivial, or unworthy of watching multiple times. His filmography is small enough, and easily available, that you should have no trouble viewing them all. Ivan’s Childhood is one of the most assured debuts ever, I think, and one of the best (anti-) war films. It’s also Tarkovsky’s most conventional, straightforward narrative film, so be prepared for things to get a lot longer, and stranger, from here on in. You’ve already had a taste of that with Solaris. Enjoy!