Biggest recent let down is Munsters. I'm in the bullseye demo and was primed to buy an LE, but it's just too simplistic for my tastes and the under playfield is cool but underwhelming given it's prominence in the design. Biggest letdown in last 5+ years is Ghostbusters. Innovative design, great art and sounds, etc. etc., F-up'ed by lack of attention to quality and geometry.
Recent surprise - Deadpool. Great fun, challenging, fantastic art.... Longer term surprise, TWD. Pinside lambasted the game but thankfully I played it for myself.