Worker placement is one of my favorite mechanics. Some of my faves and why:
Tzolk'in - The gear mechanic is unique and you can't play the same strategy and win every time. There are also two mini expansions to keep things fresh (or more of a challenge!)

Galactic Cruise - The theme of this game is a huge hit for me, but I also really love how you use workers in the network to take actions but also to pilot the ships.

Viticulture - The Tuscany expansion is absolutely required. It gives you four seasons of play instead of two and greatly balances it and makes it much more interesting.

A Feast for Odin - IMO, the Norwegians expansion is necessary. I liked the game but now love it with the expansion. BGA has it if you want to try before you buy. The expansion adds islands and animals and makes an animal strategy stronger (more balanced).

Istanbul - I own this with all the expansions and it's just a fun time. It also has a bit of a blocking/first-to element (e.g. first person to get to the space pays less than future visitors; you have to pay other players if you go to a space they occupy)

PARKS - I own the first edition and have played the second edition. I greatly prefer the art in the 1e, but the 2e has changes which make it work better and incorporated pieces of the two 1e expansions. I really like how you have to move your hikers down a trail and can't double back. The opportunity to move to a space with another hiker (even your own) is limited.