I recently put 130 hours into EU1 before burning out. It's a fun game in its relative simplicity and emptiness, and the manual was a great read for someone like me with very little historical background. One thing that really surprised me was the graphics. In screenshots I'd always thought the oldest Paradox games looked terrible - especially the weirdly drooping province borders - but when I played myself I found it looks charming!
There's still many starts and scenarios I haven't tried, but I think I'm going to dive into EU2 next.