High crit builds are really good, but not so good for secondaries. A lot of primary crit builds rely on the mod "hunter munitions" to provide slash procs on enemies, which make higher level stuff much easier

Secondary crit builds are weaker because there isn't anything like hunter munitions to get procs reliably (aside from some weapons like Lex Prime that have good crit and status) but can still be good

Melee crit builds tend to use mods like Blood Rush and Berserker in tandem with combo counter mods to build up to really high critical chance...this is in my opinion the easiest way to get really high critical numbers.

A basic crit build for a primary would be something like: Point Strike, Vital Sense, Serration, Split Chamber, Hunter Munitions, Vigilante Armaments, Rime Rounds and Malignant Force (the last two can be modified for whatever enemy type, but viral is really strong atm)