I have purchased/followed a number of Steam Early Access titles and very rarely have I been disappointed. I think the trick is, to wait a bit to see how often the devs update. There are some outliers such as RimWorld or Subnautica where updates happen only a couple times per year, but each update is game-changing and adds tons new content, features and bug-fixes.

Other titles which are still in EA but are releasing constant stream of information plus software updates:

  - Space Engineers/Medieval Engineers (weekly YT blog)
  - Rust (weekly blog)
  - Rogalia (daily to weekly Steam blog)
  - Project Zomboid (weekly blog)
  - Kenshi (between weekly and monthly changelist)
  - Factorio (weekly blog)
  - Don't Starve Together (multiplayer addition to Don't Starve)
  - DayZ (I only play maybe once per year but the blog updates seem quite frequent)

Titles which had a long EA period but ended up releasing IMHO amazingly polished products:

  - Terraria 
  - Kerbal Space Program
  - Prison Architect