You might like my course notes from CS 131, the PL course I’ve taught a few times now. It doesn’t go past the STLC and is pretty implementation focused. I’d rate it as decidedly less difficult than TAPL, which I assign as an optional, supplementary textbook.
Shriram Krishnamurthi’s PLAI book is another nice approach. It’s not written from quite the same formalist perspective as Benjamin Pierce’s TAPL. (Disclosure: Shriram was my undergraduate advisor, and Benjamin was my PhD advisor.)
Matthias Felleisen and Matthew Flatt’s Programming Languages and Lambda Calculi is another well grounded, theory-based approach, with an emphasis on abstract machines.
Jeremy Siek wrote a nice blog post about notation that might be helpful, too.