Not an exaggeration, but the base game suffered from a couple of features that felt like an after-thought and was meant to be some catch-up score for players not participating in the game. The "Zero-Bid" avenue of scoring doesn't align with the rest of the game.
This expansion does away with that and offers an additional incentive for people to be the 2nd highest bidder. It also offers a new line for you to deduct from your total expenses, so it no longer becomes as clear who will have spent the most money at the end of the game.
It adds significantly more value to the game and it should always be included each time you play QE.
Design isn't bad. The guessing of numbers to ding people on is great. The core game is good.
The absence of a theme makes this extremely dry and boring to sit through.
This offers the Basement level to build modules on. The catch is that only basement tiles can be built here. None of the other tiles (aside from Entrance tiles) can be built here, so it's quite closed off in that regard. There's no such thing as an "underground parking", which was a massive letdown.
The Basement tiles do offer some rather fun stuff, and poses as an alternative movement accelerator to conveyors... but that's about it. I don't think this offers enough for the asking price. I would skip on this unless you've already got the first three expansions and want more.
Between 4th and 5th, I'd pick up 4th, but given how little you get to really do in the game overall, I can live without the Basement tiles.
This expansion offers very late-game features. This is very catered to those who get this to the table very often and need more ways to change things up. This primarily changes up the base-game components, such as the player board, and the core module tiles (such as treatment rooms and gardens, but double-sized).
IMO the price doesn't live up to the value you get out of this (unless you play this game a lot).
Speaking purely from game design, this is a great expansion to replace portions of the base game with, since the base game tended to gear most optimal builds towards egg-laying. Oceania nerfs this and promotes spending of resources (spending on nectar for points and playing more birds in general). It makes it easier to play high-cost birds, which means a good chunk of cards are more usable.