Which Munchkin expansion should I get?

I’ve gotten really hooked on Munchkin over the last few years, but have just recently started buying the packs myself. Have then realized that there are quite a lot of different expansions available.

Having only played the regular Munckin and “The Good, the Bad and The Munchkin” I therefore turn to you for my next purchase.

Are any of the majorly different expansions way cool, or should I stick to the regular expansions before I go off into space/Cthulu/espionage/Kung Fu?

I just started another collection since mine have “disappeared” … whatever you decide, a must have is Munchkin Blender. I also really really like Cerical Errors

I’ve not really understood what the Blender does?

New rules?

There are two questions: which of the basic games, and which expansions to add to them?

Which basic game is basically a matter of which kind of genre jokes you appreciate – the gameplay is mostly the same (each has a few specific wrinkles, but the basic game mechanics is the same for all of them).

As for expansions, most of them just add a batch of cards and another minor game wrinkle. The one sorta-exception is the “Demented Dungeons” expansion for the basic game; that adds a bunch of double-sided “Dungeon” cards that add some global rule change.

The Blender expansion adds a few cards (extra “Cheats”, more low-level monsters, etc) that help mitigate one significant problem with mixed-deck games (with more races/classes/whatever in the deck, items that are tied to a race/class/whatever are less likely to be actually useful, so it’s harder to build up strength).