[Kompressa] is probably my favorite weapon in Warframe.

Notes:
This weapon takes a lot forma to build, but it's worth it!
Due to [Kompressa]'s base critical damage being only 1.8, it is more valuable to build it for raw damage rather than adding enervate and critical mods. I have done a lot of testing with enervate and have found this build surpasses any critical builds I tried.
[Galvanized Shot] is used here because it still increases direct damage to enemies. [Galvanized Shot] was switched to [Pistol Elementalist] after testing.
The explosion radius without [Primed Fulmination] isn't that huge, and just a couple direct hits from this thing easily kills Steel Path enemies. If you prefer to use this as a primer, please see the below builds or replace galvanized mods with their normal counterparts and/or add [Primed Fulmination].

Alternate Builds:

Blast and Electricity group killer:
This build is better on groups of enemies so it should be used with a crowd control frame. It looks hilarious and may crash Warframe. You have been warned.
Replace [Pistol Pestilence] with [Frostbite].
Switch [Primed Heated Charge] and [Primed Convulsion].
Replace [Accelerated Isotope] with [Pistol Elementalist] if desired.
Big boom.

For status spreading [Condition Overload] builds:
Replace [Galvanized Diffusion] with [Barrel Diffusion].
Replace [Primed Heated Charge] with [Magnetic Might].
Replace [Primed Convulsion] with [Jolt].
Replace [Lethal Torrent] with [Frostbite].
Replace [Hornet Strike] with [Scorch].
Replace Cascadia Flare with Secondary Encumber.
This will get you (bear with me) Viral, Blast, Radiation, Magnetic, and Corrosive plus whatever Secondary Encumber adds on. If that isn't enough status types I don't know what is.
This build has been very loosely tested, but seeing so many statuses is very fun.

For Corpus:
You can switch to toxin and magnetic in higher level Corpus content if needed.
Switch [Primed Heated Charge] with [Pistol Pestilence].
Replace [Primed Heated Charge] with [Deep Freeze].
Replace [Accelerated Isotope] with [Pathogen Rounds].
This will target both shields and health which isn't entirely necessary, so you can also replace Magnetic mods with [Pistol Elementalist].

Possible Replacements:
I prefer Cascadia Flare over Secondary Merciless, Secondary Enervate, and Cascadia Empowered, but use whichever you like.
[Accelerated Isotope] is a flex slot, it can be replaced with things like [Scorch], [Primed Fulmination], Rivens, or anything else you may want.
Rivens should have status chance and multishot.

I love [Kompressa]
I don't know what else to write
So have a haiku